]
The units may be found either by looking
under the category in which they are used [such as length, mass, density,
energy etc.], or else by picking one unit from an alphabetically ordered list of units. There are NO units of currency.There is an outline
of the S I; a list of its
basic defining standards and also some of its derived units; then another list of all the S I prefixes
and some notes on conventions of usage.There is a short historical note on measures generally; descriptions of the
Metric system, the U K (Imperial) system
with a statement on the implementation of 'metrication' in the U K, and the U S system.Finally
there is a list of other sources concerned with the topic of measures and
units (including other Web sites) and
also some notes about this document.
| Length | Area | Volume | Mass | Temperature |
| Density | Pressure & Stress |
Speed | Fuel Consumption |
Power |
| There is a Selection of Other Calculators also available | ||||
| To change . . | into . . | do this . . | To change . . | into . . | do this . . | |
| acres | hectares | x 0.4047 | kilograms | ounces | x 35.3 | |
| acres | sq. kilometres | / 247 | kilograms | pounds | x 2.2046 | |
| acres | sq. metres | x 4047 | kilograms | tonnes | / 1000 # | |
| acres | sq. miles | / 640 # | kilograms | tons (UK/long) | / 1016 | |
| barrels (oil) | cu.metres | / 6.29 | kilograms | tons (US/short) | / 907 | |
| barrels (oil) | gallons (UK) | x 34.97 | kilometres | metres | x 1000 # | |
| barrels (oil) | gallons (US) | x 42 # | kilometres | miles | x 0.6214 | |
| barrels (oil) | litres | x 159 | litres | cu.inches | x 61.02 | |
| centimetres | feet | / 30.48 # | litres | gallons (UK) | x 0.2200 | |
| centimetres | inches | / 2.54 # | litres | gallons (US) | x 0.2642 | |
| centimetres | metres | / 100 # | litres | pints (UK) | x 1.760 | |
| centimetres | millimetres | x 10 # | litres | pints (US liquid) | x 2.113 | |
| cubic cm | cubic inches | x 0.06102 | metres | yards | / 0.9144 # | |
| cubic cm | litres | / 1000 # | metres | centimetres | x 100 # | |
| cubic cm | millilitres | x 1 # | miles | kilometres | x 1.609 | |
| cubic feet | cubic inches | x 1728 # | millimetres | inches | / 25.4 # | |
| cubic feet | cubic metres | x 0.0283 | ounces | grams | x 28.35 | |
| cubic feet | cubic yards | / 27 # | pints (UK) | litres | x 0.5683 | |
| cubic feet | gallons (UK) | x 6.229 | pints (UK) | pints (US liquid) | x 1.201 | |
| cubic feet | gallons (US) | x 7.481 | pints (US liquid) | litres | x 0.4732 | |
| cubic feet | litres | x 28.32 | pints (US liquid) | pints (UK) | x 0.8327 | |
| cubic inches | cubic cm | x 16.39 | pounds | kilograms | x 0.4536 | |
| cubic inches | litres | x 0.01639 | pounds | ounces | x 16 # | |
| cubic metres | cubic feet | x 35.31 | ||||
| ____________ | ____________ | ______________ | _____________ | _____________ | __________ | |
| To change . . | into . . | do this . . | To change . . | into . . | do this . . | |
| square cm | sq. inches | x 0.1550 | ||||
| feet | centimetres | x 30.48 # | square feet | sq. inches | x 144 # | |
| feet | metres | x 0.3048 # | square feet | sq. metres | x 0.0929 | |
| feet | yards | / 3 # | square inches | square cm | x 6.4516 # | |
| fl.ounces (UK) | fl.ounces (US) | x 0.961 | square inches | square feet | / 144 # | |
| fl.ounces (UK) | millilitres | x 28.41 | square km | acres | x 247 | |
| fl.ounces (US) | fl.ounces (UK) | x 1.041 | square km | hectares | x 100 # | |
| fl.ounces (US) | millilitres | x 29.57 | square km | square miles | x 0.3861 | |
| gallons | pints | x 8 # | square metres | acres | / 4047 | |
| gallons (UK) | cubic feet | x 0.1605 | square metres | hectares | / 10 000 # | |
| gallons (UK) | gallons (US) | x 1.2009 | square metres | square feet | 10.76 | |
| gallons (UK) | litres | x 4.54609 # | square metres | square yards | x 1.196 | |
| gallons (US) | cubic feet | x 0.1337 | square miles | acres | x 640 # | |
| gallons (US) | gallons (UK) | x 0.8327 | square miles | hectares | x 259 | |
| gallons (US) | litres | x 3.785 | square miles | square km | x 2.590 | |
| grams | kilograms | / 1000 # | square yards | square metres | 1.196 | |
| grams | ounces | / 28.35 | tonnes | kilograms | x 1000 # | |
| hectares | acres | x 2.471 | tonnes | tons (UK/long) | x 0.9842 | |
| hectares | square km | / 100 # | tonnes | tons (US/short) | x 1.1023 | |
| hectares | square metres | x 10000 # | tons (UK/long) | kilograms | x 1016 | |
| hectares | square miles | / 259 | tons (UK/long) | tonnes | x 1.016 | |
| hectares | square yards | x 11 960 | tons (US/short) | kilograms | x 907.2 | |
| inches | centimetres | x 2.54 # | tons (US/short) | tonnes | x 0.9072 | |
| inches | feet | / 12 # | yards | metres | x 0.9144 # |
It is based upon 7 principal units, 1 in each of 7 different categories -
Category Name Abbreviation Length metre m Mass kilogram kg Time second s Electric current ampere A Temperature kelvin K Amount of substance mole mol Luminous intensity candela cd
Definitions of these basic units are given. Each of these units may take a prefix. From these basic units many other units are derived and named.
Return to the top of this document
Return to the top of this document
]
Note that prefixes may be used in conjunction with any of the above units.
Return to the top of this document
The S I allows the sizes of units to be made bigger or smaller by the use of
appropriate prefixes. For example, the electrical unit of a watt is not a big
unit even in terms of ordinary household use, so it is generally used in terms
of 1000 watts at a time. The prefix for 1000 is kilo so we use
kilowatts[kW] as our unit of measurement. For makers of electricity, or bigger
users such as industry, it is common to use megawatts[MW] or even gigawatts[GW].
The full range of prefixes with their [symbols or abbreviations] and their
multiplying factors which are also given in other forms is Return to the top of this document
There are various rules laid down for the use of the SI and its units as well
as some observations to be made that will help in its correct use.
Return to the top of this document
The Prefixes of the S I
yotta [Y] 1 000 000 000 000 000 000 000 000 = 10^24
zetta [Z] 1 000 000 000 000 000 000 000 = 10^21
exa [E] 1 000 000 000 000 000 000 = 10^18
peta [P] 1 000 000 000 000 000 = 10^15
tera [T] 1 000 000 000 000 = 10^12
giga [G] 1 000 000 000 (a thousand millions = a billion)
mega [M] 1 000 000 (a million)
kilo [k] 1 000 (a thousand)
hecto [h] 100
deca [da]10
1
deci [d] 0.1
centi [c] 0.01
milli [m] 0.001 (a thousandth)
micro [µ] 0.000 001 (a millionth)
nano [n] 0.000 000 001 (a thousand millionth)
pico [p] 0.000 000 000 001 = 10^-12
femto [f] 0.000 000 000 000 001 = 10^-15
atto [a] 0.000 000 000 000 000 001 = 10^-18
zepto [z] 0.000 000 000 000 000 000 001 = 10^-21
yocto [y] 0.000 000 000 000 000 000 000 001 = 10^-24
[µ] the symbol used for micro is the Greek letter known as 'mu'
Nearly all of the S I prefixes are multiples or sub-multiples of 1000.
However, these are inconvenient for many purposes and so hecto,
deca, deci, and centi are also used.
deca also
appears as deka [da] or [dk] in the USA and Contintental Europe.
So much for standards!
Conventions of Usage in the S I
In England units of measurement were not properly standardised until the 13th
century, though variations (and abuses) continued until long after that. For
example, there were three different gallons (ale, wine and corn) up until 1824
when the gallon was standardised.
In the U S A the system of weights and measured first adopted was that of the
English, though a few differences came in when decisions were made at the time
of standardisation in 1836. For instance, the wine-gallon of 231 cubic inches
was used instead of the English one (as defined in 1824) of about 277 cubic
inches. The U S A also took as their standard of dry measure the old Winchester
bushel of 2150.42 cubic inches, which gave a dry gallon of nearly 269 cubic
inches.
Even as late as the middle of the 20th century there were some differences in
UK and US measures which were nominally the same. The UK inch measured 2.53998
cm while the US inch was 2.540005 cm. Both were standardised at 2.54 cm in July
1959, though the U S continued to use 'their' value for several years in land
surveying work - this too is slowly being metricated.
In France the metric system officially started in June 1799 with the declared
intent of being 'For all people, for all time'. The unit of length was the metre
which was defined as being one ten-millionth part of a quarter of the earth's
circumference. The production of this standard required a very careful survey to
be done which took several years. However, as more accurate instruments became
available so the 'exactness' of the standard was called into question. Later
efforts were directed at finding some absolute standard based on an observable
physical phenomenon. Over two centuries this developed into the S I. So maybe
their original slogan was more correct than anyone could have foreseen then.
Return to the top of this document
A Brief History of Measurement
One of the
earliest types of measurement concerned that of length. These measurements were
usually based on parts of the body. A well documented example (the first) is the
Egyptian cubit which was derived from the length of the arm from the elbow to
the outstretched finger tips. By 2500 BC this had been standardised in a royal
master cubit made of black marble (about 52 cm). This cubit was divided into 28
digits (roughly a finger width) which could be further divided into fractional
parts, the smallest of these being only just over a millimetre.
Metric System of Measurements
Length Area
10 millimetres = 1 centimetre 100 sq. mm = 1 sq. cm
10 centimetres = 1 decimeter 10 000 sq. cm = 1 sq. metre
10 decimetres = 1 metre 100 sq. metres = 1 are
10 metres = 1 decametre 100 ares = 1 hectare
10 decametres = 1 hectometre 10 000 sq. metres = 1 hectare
10 hectometres = 1 kilometre 100 hectares = 1 sq. kilometre
1000 metres = 1 kilometre 1 000 000 sq. metres = 1 sq. kilometre
Volume Capacity
1000 cu. mm = 1 cu. cm 10 millilitres = 1 centilitre
1000 cu. cm = 1 cu. decimetre 10 centilitree = 1 decilitre
1000 cu. dm = 1 cu. metre 10 decilitres = 1 litre
1 million cu. cm = 1 cu. metre 1000 litres = 1 cu. metre
Mass
1000 grams = 1 kilogram
1000 kilograms = 1 tonne
The distinction between 'Volume' and 'Capacity' is artificial and kept
here only for historic reasons.
A millitre is a cubic centimetre and a cubic decimetre is
a litre. But see under 'Volume' for problems with the litre.
Return to the top of this document
1 yard = 0.9144 metres - same as US Return to the top of this document
The U K (Imperial) System of Measurements
Length Area
12 inches = 1 foot 144 sq. inches = 1 square foot
3 feet = 1 yard 9 sq. feet = 1 square yard
22 yards = 1 chain 4840 sq. yards = 1 acre
10 chains = 1 furlong 640 acres = 1 square mile
8 furlongs = 1 mile
5280 feet = 1 mile
1760 yards = 1 mile Capacity
20 fluid ounces = 1 pint
Volume 4 gills = 1 pint
1728 cu. inches = 1 cubic foot 2 pints = 1 quart
27 cu. feet = 1 cubic yard 4 quarts = 1 gallon (8 pints)
Mass (Avoirdupois)
437.5 grains = 1 ounce Troy Weights
16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
8 stones = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
20 cwt = 1 ton (2240 pounds)
Apothecaries' Measures Apothecaries' Weights
20 minims = 1 fl.scruple 20 grains = 1 scruple
3 fl.scruples = 1 fl.drachm 3 scruples = 1 drachm
8 fl.drachms = 1 fl.ounce 8 drachms = 1 ounce (480 grains)
20 fl.ounces = 1 pint 12 ounces = 1 pound (5760 grains)
The old Imperial (now UK) system was originally defined by three standard
measures - the yard, the pound and the gallon which were held in London. They
are now defined by reference to the S I measures of the metre, the kilogram and
the litre. These equivalent measures are exact.
1 pound = 0.453 592 37 kilograms -
same as US
1 gallon = 4.546 09 litres
Note particularly that the UK gallon
is a different size to the US gallon so that NO liquid measures of the same name
are the same size in the UK and US systems.
Also that the ton(UK) is 2240
pounds while a ton(US) is 2000 pounds. These are also referred to as a long ton
and short ton respectively.
There have been three major Weights and Measures Acts in recent times (1963,
1976 and 1985) all gradually abolishing various units, as well re-defining the
standards. All the Apothecaries' measures are gone, and of the Troy measures,
only the ounce remains. Currently legislation has decreed that -
From the 1st October 1995, for economic, public health, public safety and
administrative purposes, only metric units are allowed EXCEPT that -
The following may continue to be used WITHOUT time limit -
That is how the legislation is framed. In common usage the 'old' units are
still very apparent.
Return to the top of this document
1 yard = 0.9144 metres - same as UK Return to the top of this document
N - O - PQ - R - S - T - UVW - XYZ Return to the
top of this document
The S I unit of length is the metre. To change any of these other
units of length into their equivalent values in metres use the operation
and conversion factor given. Those marked with # are exact. Other values
are given to an appropriate degree of accuracy. Where some uncertainty is
indicated it means that a good idea of the size of the unit can be given but
that a better value would depend upon knowing the period and/or culture in which
the unit was being used. Return to the
top of this document
The S I unit of area is the square metre. To change any of these other
units of area into their equivalent values in square metres use the
operation and conversion factor given. Those marked with # are exact.
Other values are given to an appropriate degree of accuracy. Where some
uncertainty is indicated it means that a good idea of the size of the unit can
be given but that a better value would depend upon knowing the period and/or
culture in which the unit was being used. Return to the
top of this document
The S I unit of volume is the cubic metre. However, this seems to be much
less used than the litre (1000 litres = 1 cubic metre).To change any of
these other units of volume into their equivalent values in litres use
the operation and conversion factor given. Those marked with # are exact.
Other values are given to an appropriate degree of accuracy. The S I unit of mass is the kilogram. To change any of these other
units of mass into their equivalent values in kilograms use the operation
and conversion factor given. Those marked with # are exact. Other values
are given to an appropriate degree of accuracy. There have been five main temperature scales, each one being named after the
person who invented it. Line density is a measure of mass per unit length. The S I compatible unit of
line density is kilograms/metre. A major use of line density is in the
textile industry to indicate the coarseness of a yarn or fibre. For that purpose
the SI unit is rather large so the preferred unit there is the tex. (1
tex = 1 gram/kilometre) To change any of these other units of line density into
their equivalent values in kilograms/metre use the operation and
conversion factor given. Those marked with # are exact. Other values are
given to an appropriate degree of accuracy. Density is the shortened term generally used in place of the more accurate
description volumetric density.It is a measure of mass per unit volume.
The S I compatible unit of density is kilograms/cubic metre. However,
this a rather large unit for most purposes (iron is over 7000, wood is about 600
and even cork is over 200). A much more useful size of unit is
kilograms/litre (for which the previous values then become 7, 0.6 and 0.2
respectively). This unit also has the great advantage of being numerically
unchanged for grams/cubic centimetre and tonnes/cubic metre (or megagrams/cubic
metre). To change any of these other units of density into their equivalent
values in kilograms/litre use the operation and conversion factor given.
Those marked with # are exact. Other values are given to an appropriate
degree of accuracy. The S I unit of energy or work is the joule. To change any of these
other units of energy or work into their equivalent values in joules use
the operation and conversion factor given. Those marked with # are exact.
Other values are given to an appropriate degree of accuracy. The S I unit of force is the newton. To change any of these other
units of force into their equivalent values in newtons use the operation
and conversion factor given. Those marked with # are exact. Other values
are given to an appropriate degree of accuracy. Fuel consumption of any means of transport (car, aeroplane, ship etc.) that
uses fuel is a measure giving the relationship between the distance travelled
for an amount of fuel used. The most common example is the car where it is
usually expressed (in English-speaking countries) in miles per gallon. The S I unit of power is the watt. To change any of these other units
of energy or work into their equivalent values in watts use the operation
and conversion factor given. Those marked with # are exact. Other values
are given to an appropriate degree of accuracy. The S I unit of pressure is the pascal. The units of pressure are
defined in the same way as those for stress - force/unit area. To change any of
these other units of pressure (or stress) into their equivalent values in
pascals use the operation and conversion factor given. Those marked with #
are exact. Other values are given to an appropriate degree of accuracy.
Measures based on water assume a density of 1 kg/litre - a value which rarely
matched in the real world, though the error is small. The S I compatible unit of speed is metres/second. To change any of
these other units of speed into their equivalent values in metres/second
use the operation and conversion factor given. Those marked with # are
exact. Other values are given to an appropriate degree of accuracy. The spread rate of a substance is a measure of how much of it there is
covering a unit area. The 'how much' can be measured by volume or by mass. The S
I compatible unit of spread rate by mass is kilograms/square metre. It is
also a measure of area density (mass/unit area) and is similar to - but not the
same as - pressure, which is force/unit area. For the rainfall conversions a
density of 1 kg/litre has been assumed. To change any of these other units of
spread rate into their equivalent values in kilograms/square metre use
the operation and conversion factor given. Those marked with # are exact.
Other values are given to an appropriate degree of accuracy. The conversion for
rainfall assumes a density of 1 kg/litre which is accurate enough for all
practical purposes. The spread rate of a substance is a measure of how much of it there is
covering a unit area. The 'how much' can be measured by volume or by mass. The S
I compatible unit of spread rate by volume is cubic metres/square metre.
However, this is a rather large unit for most purposes and so litres/square
metre is often preferred. To change any of these other units of spread rate into
their equivalent values in litres/square metre use the operation and
conversion factor given. Those marked with # are exact. Other values are
given to an appropriate degree of accuracy. The S I compatible unit of torque is the newton metre. To change any
of these other units of torque into their equivalent values in newton
metres use the operation and conversion factor given. Those marked with #
are exact. Other values are given to an appropriate degree of accuracy. Conversion Tables of Units for Science and Engineering The Dent Dictionary of Measurement The Economist Desk Companion The Encyclopaedia Britannica World Weights and Measures British Weights and Measures The World of Measurements Scientific Unit Conversion The first to be considered must the Official SI Web-site in
France.
In the UK a very good place to make a start
is the Metrication Resource Site
run by Chris Keenan. In the USA the National Institute of Standards and
Technology (NIST) is excellent, and there is no shortage of information
concerning units and their conversion. There is even an excellent 86-page book
on the subject (SP 811) which can be read on-line or downloaded and printed out
- but note that Adobe Acrobat Reader is needed. An excellent A to Z
of units is available from this site run by Russ Rowlett at the
University of North Carolina.
Another account of metrication and associated items which has, in addition,
some very good pages on historic measures (Anglo-Saxon, Biblical etc.) is
provided by Jack
Proot (in Canada)
The International Standards
Organisation] [I S O] based in Switzerland, is responsible for the
world-wide publication of standards for just about anything for which standards
can be set. Whilst none of the actual data is online, details of the work of ISO
and the publications they produce are. They also give many references to other
organisations concerned with standards. Return to the
top of this document
Return to the
top of this document
Metrication in the U K
may be used until 31st December
1999.
Sports are exempt
from all of this, but most of them have (voluntarily) changed their relevant
regulations into statements of equivalent metric measures.
The U S System of Measurements
Most of the US
system of measurements is the same as that for the UK. The biggest differences
to be noted are in Capacity which has both liquid and dry measures as well as
being based on a different standard - the US liquid gallon is smaller than the
UK gallon. There is also a measurement known at the US survey foot. It is
gradually being phased out as the maps and land plans are re-drawn under
metrication. (The changeover is being made by putting 39.37 US survey feet = 12
metres) Length Area
12 inches = 1 foot 144 sq. inches = 1 square foot
3 feet = 1 yard 9 sq. feet = 1 square yard
220 yards = 1 furlong 4840 sq. yards = 1 acre
8 furlongs = 1 mile 640 acres = 1 square mile
5280 feet = 1 mile 1 sq.mile = 1 section
1760 yards = 1 mile 36 sections = 1 township
Volume
1728 cu. inches = 1 cubic foot
27 cu. feet = 1 cubic yard
Capacity (Dry) Capacity (Liquid)
16 fluid ounces = 1 pint
2 pints = 1 quart 4 gills = 1 pint
8 quarts = 1 peck 2 pints = 1 quart
4 pecks = 1 bushel 4 quarts = 1 gallon (8 pints)
Mass
437.5 grains = 1 ounce Troy Weights
16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
100 pounds = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
20 cwt = 1 ton (2000 pounds)
Apothecaries' Measures Apothecaries' Weights
60 minims = 1 fl.dram 20 grains = 1 scruple
8 fl.drams = 1 fl.ounce 3 scruples = 1 dram
16 fl.ounces = 1 pint 8 drams = 1 ounce (480 grains)
12 ounces = 1 pound (5760 grains)
As with the UK system these measures were originally defined by physical
standard measures - the yard, the pound, the gallon and the bushel.They are now
all defined by reference to the S I measures of the metre, the kilogram and the
litre. These equivalent measures are exact.
1 pound = 0.453 592 37 kilograms -
same as UK
1 gallon (liquid) = 3.785 411 784 litres
1 bushel = 35.239 070
166 88 litres
Note particularly that the US gallon is a different size to
the UK gallon so that NO liquid measures of the same name are the same size in
the US and UK systems.
Also that the ton(US) is 2000 pounds while a ton(UK)
is 2240 pounds. These are also referred to as a short ton and long ton
respectively.
Note than in matters concerned with land measurements, for the
most accurate work, it is necessary to establish whether the US survey measures
are being used or not.
Categories of Units
Return to the top of this
document
List of Units
The units are listed in alphabetical order but scanning can be speeded up by
selecting the initial letter of the unit from these individual letters or
groups
A - B - C - D - E - F - G - H - IJ - K - L - M
A
B
C
D
E
F
G
H
IJ
K
L
M
N
O
PQ
R
S
T
UVW
XYZ
Length
angstroms divide by 10 000 000 000 #
astronomical units x 149 598 550 000
barleycorns x 0.008 467
centimetres x 0.01 #
chains (surveyors') x 20.1168 #
cubits x (0.45 to 0.5)
ells (UK) x 0.875 (but many variations)
ems (pica) x 0.004 233 3
fathoms x 1.8288 #
feet (UK and US) x 0.3048 #
feet (US survey) x 0.304 800 609 6
furlongs x 201.168 #
hands x 0.106 #
inches x 0.0254 #
kilometres x 1000 #
leagues x (4000 to 5000)
light years x 9 460 500 000 000 000
links (surveyors') x 0.201 168 #
metres [m] 1
microns (=micrometres) x 0.000 001 #
miles (UK and US) x 1609.344 #
miles (nautical) x 1852 #
parsecs x 30 856 770 000 000 000
perch (=rods or poles) x 5.0292 #
picas (computer) x 0.004 233 333
picas (printers') x 0.004 217 518
points (computer) x 0.000 352 777 8
points (printers') x 0.000 351 459 8
yards x 0.9144 #
Note than in matters concerned with land measurements, for the most
accurate work, it is necessary to establish whether the US survey measures are
being used or not.
Area
acres x 4046.856 422 4 #
ares x 100 #
circular inches x 0.000 506 707 479
hectares x 10 000 #
hides x 485 000 (with wide variations)
roods x 1011.714 105 6 #
square centimetres x 0.000 1 #
square feet (UK and US) x 0.092 903 04 #
square feet (US survey) x 0.092 903 411 613
square inches x 0.000 645 16 #
square kilometres x 1 000 000 #
square metres 1
square miles x 2 589 988.110 336 #
square millimetres x 0.000 001 #
squares (of timber) x 9.290 304 #
square rods (or poles) x 25.292 852 64 #
square yards x 0.836 127 36 #
townships x 93 239 571.972
Note than in matters concerned with land measurements, for the most
accurate work, it is necessary to establish whether the US survey measures are
being used or not.
Volume or Capacity
The
litre. There can be some ambiguity about the size of the litre. In 1901
it was defined by reference to a kilogram of pure water under certain particular
conditions. (This was similar to the way the old UK gallon was set.) In 1964 it
was re-defined as a common usage term for a cubic decimetre. They differ very
slightly and for really accurate work, to avoid any possible confusion, it is
recommended that the litre is not used . It is used here as being a cubic
decimetre. barrels (oil) x 158.987 294 928 #
bushels (UK) x 36.368 72 #
bushels (US) x 35.239 070 166 88 #
centilitres x 0.01 #
cubic centimetres x 0.001 #
cubic decimetres 1
cubic decametres x 1 000 000 #
cubic feet x 28.316 846 592 #
cubic inches x 0.016 387 064 #
cubic metres x 1000 #
cubic millimetres x 0.000 001 #
cubic yards x 764.554 857 984 #
decilitres x 0.1 #
fluid ounces (UK) x 0.028 413 062 5 #
fluid ounces (US) x 0.029 573 529 562 5 #
gallons (UK) x 4.546 09 #
gallons, dry (US) x 4.404 883 770 86 #
gallons, liquid (US) x 3.785 411 784 #
litres [l or L] 1
litres (1901 - 1964) x 1.000 028
millilitres x 0.001 #
pints (UK) x 0.568 261 25 #
pints, dry (US) x 0.550 610 471 357 5 #
pints, liquid (US) x 0.473 176 473 #
quarts (UK) x 1.136 522 5 #
quarts, dry (US) x 1.101 220 942 715 #
quarts, liquid (US) x 0.946 352 946 #
Return to the
top of this document
Mass (or Weight)
carats, metric x 0.000 2 #
grains x 0.000 064 798 91 #
grams x 0.001 #
hundredweights, long x 50.802 345 44 #
hundredweights, short x 45.359 237 #
kilograms [kg] 1
ounces, avoirdupois x 0.028 349 523 125 #
ounces, troy x 0.031 103 476 8 #
pounds x 0.453 592 37 #
slugs (or g-pounds) x 14.593 903
stones x 6.350 293 18 #
tons (UK or long) x 1016.046 908 8 #
tons (US or short) x 907.184 74 #
tonnes x 1000 #
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Temperature
G D FAHRENHEIT (1686-1736) a German physicist, in
about 1714 proposed the first practical scale. He called the freezing-point of
water 32 degrees (so as to avoid negative temperatures) and the boiling-point
212 degrees.
R A F de REAUMUR (1673-1757) A French entomologist, proposed a
similar scale in 1730, but set the freezing-point at 0 degrees and the
boiling-point at 80 degrees. This was used quite a bit but is now
obsolete.
Anders CELSIUS (1701-1744) a Swedish astronomer, proposed the
100-degree scale (from 0 to 100) in 1742. This was widely adopted as the
centigrade scale. But since grades and centigrades were also measures of angle,
in 1948 it officially became the Celsius scale. Also, the S I system of units
gives preference to naming units after people where possible.
William
Thomson, 1st Lord KELVIN (1824-1907) a Scottish mathematician and physicist,
worked with J P Joule - about 1862 - to produce an absolute scale of temperature
based on laws of heat rather than the freezing/boiling-points of water. This
work produced the idea of 'absolute zero', a temperature below which it was not
possible to go. Its value is -273.15 degrees on the Celsius scale.
William J
M RANKINE (1820-1872) a Scottish engineer and scientist, promoted the Kelvin
scale in its Fahrenheit form, when the equivalent value of absolute zero is
-459.67 degrees Fahrenheit.
Nowadays, while scientists use the KELVIN scale,
the CELSIUS scale is the preferred scale in our everyday lives. However, the
Fahrenheit scale is still widely used and there frequently is a need to be able
to change from one to the other.
To change temperature given in Fahrenheit
(F) to Celsius (C) Start with (F); subtract 32; multiply by 5; divide by 9; the answer is (C)
To change temperature given in Celsius (C) to Fahrenheit
(F) Start with (C); multiply by 9; divide by 5; add on 32; the answer is (F)
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Line density
denier divide by 9 000 000 #
drex divide by 10 000 000 #
grams/centimetre divide by 10 #
grams/kilometre (tex) divide by 1 000 000 #
grams/metre divide by 1000 #
grams/millimetre 1
kilograms/kilometre divide by 1000 #
kilograms/metre 1
milligrams/centimetre divide by 10 000 #
milligrams/millimetre divide by 1000 #
ounces/inch x 1.116 125
ounces/foot x 0.093 01
pounds/inch x 17.858
pounds/foot x 1.488 164
pounds/yard x 0.496 055
pounds/mile x 0.000 281 849
tex divide by 1 000 000 #
tons(UK)/mile x 0.631 342
tons(US)/mile x 0.563 698
tonnes/kilometre 1
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Density
grains/gallon(UK) divide by 70 156
grains/gallon(US) divide by 58 418
grams/cubic centimetre 1
grams/litre divide by 1000 #
grams/millilitre 1
kilograms/cubic metre divide by 1000 #
megagrams/cubic metre 1
milligrams/millilitre divide by 1000 #
milligrams/litre divide by 1 000 000 #
kilograms/litre 1
ounces/cubic inch x 1.729 994 044
ounces/gallon(UK) x 0.006 236 023
ounces/gallon(US) x 0.007 489 152
pounds/cubic inch x 27.679 904
pounds/cubic foot x 0.016 018 463
pounds/gallon(UK) x 0.099 776 373
pounds/gallon(US) x 0.119 826 427
tonnes/cubic metre 1
tons(UK)/cubic yard x 1.328 939 184
tons(US)/cubic yard x 1.186 552 843
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Energy or work
There is a lot of room for
confusion in some of the units used here. The calorie can take 5
different values and, while these do not vary by very much, for accurate work it
is necessary to specify which calorie is being used.
The 5 calories are known
as the International Table calorie - cal(IT); the thermochemical calorie -
cal(th); the mean calorie - cal(mean); the 15 degree C calorie - cal(15C); and
the 20 degree C calorie - cal(20C).
As a further complication, in working
with food and expressing nutritional values, the unit of a Calorie (capital
C) is often used to represent 1000 calories, and again it is necessary to
specify which calorie is being used for that.
The British thermal unit
(Btu) can also take different values and they are named in a similar way to the
calorie, that is
British thermal units(IT)x 1055.056
Btu (th) x 1054.350
Btu (mean) x 1055.87
calories - cal (IT) x 4.1868 #
- cal (th) x 4.184 #
- cal (mean) x 4.190 02
- cal (15C) x 4.185 80
- cal (20C) x 4.181 90
Calorie (food) x 4186 (approx.)
centigrade heat units x 1900.4
ergs divide by 10 000 000 #
foot pounds-force x 1.355 817
foot poundals x 0.042 140
gigajoules [GJ] x 1000 000 000 #
horsepower hours x 2 684 520 (approx.)
joules [J] 1
kilocalories (IT) x 4186.8 #
kilocalories (th) x 4184 #
kilogram-force metres x 9.806 65 #
kilojoules [kJ] x 1000 #
kilowatt hours [kWh] x 3 600 000 #
megajoules [MJ] x 1 000 000 #
newton metres [Nm] x 1 #
therms x 105 500 000 (approx.)
watt seconds [Ws] 1
watt hours [Wh] x 3600 #
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Force
dynes divide by 100 000 #
kilograms force x 9.806 65 #
kilonewtons [kN] x 1000 #
kips x 4448.222
meganewtons [MN] x 1 000 000 #
newtons [N] 1
pounds force x 4.448 222
poundals x 0.138 255
sthenes (=kN) x 1000
tonnes force x 9806.65 #
tons(UK) force x 9964.016
tons(US) force x 8896.443
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Fuel Consumption
It
could also be expressed in gallons per mile. However, for a car the latter
method gives a rather small figure: 35 miles per gallon is about 0.0286 gallons
per mile. In that case it would be better to give a figure for 100 miles, so it
would be 2.86 gallons per 100 miles. That is the metric way of expressing fuel
consumption - as litres per 100 kilometres.
From regular enquiries it
appears that in real life people are using all sorts of ways of expressing their
fuel consumption, so this section (unlike all the others) tries to cover as many
ways as possible. All the values are given to an accuracy of 4 significant
figures. To change into
miles per gallon (UK) miles per gallon (US) multiply by 0.833
miles per gallon (UK) miles per litre multiply by 0.22
miles per litre miles per gallon (UK) multiply by 4.546
miles per gallon (UK) kilometres per litre multiply by 0.354
miles per gallon (US) miles per gallon (UK) multiply by 1.2
miles per gallon (US) miles per litre multiply by 0.2642
miles per litre miles per gallon (US) multiply by 3.785
miles per gallon (US) kilometres per litre multiply by 0.4251
X miles per gallon gallons per 100 miles: divide 100 by X
(both gallons must of the same type)
X miles per gallon (UK) litres per 100 km: divide 282.5 by X
X miles per gallon (US) litres per 100 km: divide 235.2 by X
X km per litre litres per 100 km: divide 100 by X
X miles per litre litres per 100 km: divide 62.14 by X
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Power
Since power is a measure of the rate at
which work is done, the underlying units are those of work or energy,
and that section should be looked at for explanations concerning the
calorie and Btu. In this section the (IT) values have been
used.
In this section it is the horsepower which provides confusion.
Just like the calorie, it can take 5 different values, and these are identified
as necessary by the addition of (boiler), (electric), (metric), (UK) and
(water). Unlike the calorie (whose 5 values are reasonably close to each
other), the horsepower has 4 which are close and 1 (boiler) which is
considerably different - it is about 13 times bigger than the others - but it
seems to be very little used.
Btu/hour x 0.293 071
Btu/minute x 17.584 267
Btu/second x 1055.056
calories/hour x 0.001 639
calories/minute x 0.069 78
calories/second x 4.1868 #
ft lb-force/minute x 0.022 597
ft lb-force/second x 1.355 82
gigawatts [GW] x 1 000 000 000
horsepower (electric) x 746 #
horsepower (metric) x 735.499
watts [W] 1
joules/hour divide by 3600 #
joules/minute divide by 60 #
joules/second 1
kilocalories/hour x 1.163
kilocalories/minute x 69.78
kg-force metres/hour x 0.002 724
kg-force metres/minute x 0.163 444
kilowatts [kW] x 1000 #
megawatts [MW] x 1 000 000 #
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Pressure or Stress
atmospheres x 101 325 #
bars x 100 000 #
centimetres of mercury x 1333.22
centimetres of water x 98.066 5 #
feet of water x 2989.066 92 #
hectopascals [hPa] x 100 #
inches of water x 249.088 91 #
inches of mercury x 3386.388
kg-force/sq.centimetre x 98 066.5 #
kg-force/sq.metre x 9.806 65 #
kilonewton/sq.metre x 1000 #
kilopascal [kPa] x 1000 #
kips/sq.inch x 6 894 760
meganewtons/sq.metre x 1 000 000 #
metres of water x 9806.65 #
millibars x 100 #
pascals [Pa] 1
millimetres of mercury x 133.322
millimetres of water x 9.806 65 #
newtons/sq.centimetre x 10 000
newtons/sq.metre 1
newtons/sq.millimetre x 1 000 000 #
pounds-force/sq.foot x 47.880
pounds-force/sq.inch x 6894.757
poundals/sq.foot x 1.448 16
tons(UK)-force/sq.foot x 107 251
tons(UK)-force/sq.inch x 15 444 256
tons(US)-force/sq.foot x 95 760
tons(US)-force/sq.inch x 13 789 500
tonnes-force/sq.cm x 98 066 500 #
tonnes-force/sq.metre x 9806.65 #
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Speed
centimetres/minute divide by 6000 #
centimetres/second divide by 100 #
feet/hour divide by 11 811
feet/minute x 0.005 08 #
feet/second x 0.3048 #
inches/minute divide by 2362.2
inches/second x 0.0254 #
kilometres/hour divide by 3.6 #
kilometres/second x 1000 #
knots x 0.514 444
Mach number x 331.5
metres/hour divide by 3600 #
metres/minute divide by 60 #
metres/second [m/s] 1
miles/hour x 0.447 04 #
miles/minute x 26.8224 #
miles/second x 1609.344 #
yards/hour divide by 3937
yards/minute x 0.015 24 #
yards/second x 0.9144 #
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Spread Rate (by mass)
grams/sq.centimetre x 10 #
grams/sq.metre divide by 1000 #
inches of rainfall x 2.54
kilograms/hectare divide by 10 000 #
kilograms/sq.centimetre x 10 000 #
milligrams/sq.metre divide by 1000 #
millimetres of rainfall 1
kilograms/sq.metre 1
ounces/sq.foot x 0.305 152
ounces/sq.inch x 43.942
ounces/sq.yard divide by 49.494
pounds/acre divide by 8921.791
pounds/sq.foot x 4.882 428
pounds/sq.inch x 703.07
pounds/sq.yard x 0.542 492
tonnes/hectare divide by 10 #
tons(UK)/acre divide by 3.982 942
tons(US)/acre divide by 4.460 896
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Spread Rate (by volume)
cubic feet/acre divide by 142.913
cubic inches/sq.yard divide by 51.024
cubic yards/sq.mile divide by 3387.577
cubic metres/hectare divide by 10 #
cubic metres/sq.km divide by 1000 #
cubic metres/sq.metre x 1000 #
fl. ounces(UK)/sq.yard divide by 29.428
litres/square metre 1
gallons(UK)/acre divide by 890.184
gallons(US)/acre divide by 1069.066
gallons(UK)/hectare divide by 2199.692
gallons(US)/hectare divide by 2641.721
inches of rainfall x 25.4 #
litres/hectare divide by 10 000 #
millilitres/sq.metre divide by 1000 #
millimetres of rainfall 1
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Torque
dyne centimetres divide by 10 000 000 #
gram-force centimetres x 0.000 098 066 5 #
kg-force centimetres x 0.098 066 5 #
kg-force metres x 9.806 65 #
newton centimetres divide by 100 #
newton metres [Nm] 1
ounce-force inches divide by 141.612
pound-force inches x 0.112 984
pound-force feet x 1.355 818
poundal feet x 0.042 140
ton(UK)-force feet x 3 037.032
ton(US)-force feet x 2 711.636
tonne-force metres x 9 806.65 #
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Other Sources in Books
by Ari
L Horvath
Macmillan Reference Books, London, 1986 (147 pages)
ISBN 0
333 40857 8
Probably the most comprehensive set of conversion factors
in print, covering both old and modern units. There are 77 tables covering
categories from Length to Radiation dosage. The Length table alone lists
107 units together with the conversion factors needed to change each one
into metres.
by Darton and Clark
J M
Dent, London, 1994 (538 pages)
ISBN 0 460 861379
Very comprehensive
coverage of all kinds of units (including currencies), ordered in
conventional dictionary form, and giving several conversion factors.
Random Century, London, 1992
(272 pages)
ISBN 0 7126 9816 7
A handy compendium of units used in
Science, Medicine, Engineering, Industry, Commerce, Finance and many other
places, together with all the necessary conversion factors. There is also
much other incidental (but related) information.
The modern E B has many
references to units, but extensive use needs to be made of the index to
find them all. It gives a wide selection of weights and measures from
countries around the world and the appropriate conversion factors.
Statistical Office of the United
Nations, New York 1955 (225 pages)
A very comprehensive survey of each
country in the world (as it was then) from Aden to Zanzibar, giving the
units used in each for Length, Area and Capacity with their British and
Metric equivalents. There is an appendix on the measures used for selected
commodities. Currencies are also given. The indexes are very thorough.
The Weights and Measures of England
by R D Connor
H M S
O, London, 1987 (422 pages)
ISBN 0 460 86137 9
A scholarly and
detailed account of the history of the development of the British
(Imperial) system of weights and measures from the earliest times.
by R E Zupko
A history
from Antiquity to the Seventeenth Century
The University of
Wisconsin Press, 1977 [248 pages]
ISBN 0 299 07340 8
The actual
history occupies only 100 pages. There is then an extensive list of the
various units used in commerce, tables of many pre-Imperial units, a long
list of pre-metric measures used in Europe together with their British and
metric equivalents, and nearly 40 pages giving other sources.
by H Arthur Klein
Allen and
Unwin, London, 1975 (736 pages)
ISBN 0 04 500024 7
A very readable
and comprehensive account of the history of units used in measuring, from
the earliest known beginnings and around the world.
by Francois
Cardarelli
Springer-Verlag, London, 1997 (456 pages)
ISBN
3-540-76022-9
It claims "This practical manual aims to be the most
comprehensive work on the subject of unit conversion. It contains more
than 10 000 precise conversion factors."
It is certainly a very chunky
and compact (= handy-sized) book. Comprehensive it certainly is but still
not complete. However, with its very wide coverage, both historical and
modern, it should certainly satisfy nearly all
users.Other Sources on the World Wide
Web
The problem is simply: which one best
suits the purpose?
It covers just about everything one could want to know
about metrication and, if not covered, gives links to sites where you might find
it. Current state of progress, legislation, directives, arguments (for and
against), conversions, and many other points of interest, all get a mention.
The US Metric Association is
also a good starting point which provides a wealth of links to other suitable
sites.
Notes
This dictionary is not
meant to be encyclopaedic in its coverage, and there are many many more
units which are not touched upon, but it is hoped that all 'ordinary'
needs are covered. The many references to other sources, both in books
and on-line should take care of anything beyond that.
Finally, I must
thank all of those who wrote with suggestions (and corrections!) after
reading the earlier editions.