yards per hour etc.
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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.
Call up a Conversion
Calculator for
Units of
Length OR the Background Notes on
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 0.1016 #
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.
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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.
Call up a Conversion
Calculator for
Units of
Area OR the Background Notes on
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.
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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 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 redefined
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.
Call up a Conversion
Calculator for
Units of
Volume OR the Background Notes on
Volume
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 #
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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.
Call up a Conversion
Calculator for
Units of
Mass OR the Background Notes on
Mass
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 gpounds) 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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There have been five main
temperature scales, each one being named after the person who
invented it.
G D FAHRENHEIT (16861736) a German physicist, in about 1714
proposed the first practical scale. He called the freezingpoint
of water 32 degrees (so as to avoid negative temperatures) and the
boilingpoint 212 degrees.
R A F de REAUMUR (16731757) A French entomologist, proposed a
similar scale in 1730, but set the freezingpoint at 0 degrees and
the boilingpoint at 80 degrees. This was used quite a bit but is
now obsolete.
Anders CELSIUS (17011744) a Swedish astronomer, proposed the
100degree 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 1947 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 (18241907) 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/boilingpoints 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 (18201872) 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.
Call up a Conversion
Calculator for
Units of
Temperature OR the Background Notes on
Temperature
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 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.
Call up a
Conversion Calculator for
Units
of Line Density OR the Background Notes on
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 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.
Call up a Conversion
Calculator for
Units of
Density OR the Background Notes on
Density
grains/gallon(UK) divide by 70 157
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 27.679 905
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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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
Btu (IT), (th), etc. Also note that the therm
is 100 000 Btu so its exact size depends on which Btu
is being used.
Call up a Conversion
Calculator for
Units
of Energy OR the Background Notes on
Energy
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.
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 poundsforce x 1.355 818
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 #
kilogramforce 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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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.
Call up a Conversion
Calculator for
Units
of Force OR the Background Notes on
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 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
Englishspeaking countries) in miles per gallon.
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.
Call up a
Conversion Calculator for
Units of
Fuel Consumption OR the Background Notes on
Fuel Consumption
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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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.
Call up a Conversion Calculator
for
Units of Power OR the Background Notes on
Power
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.
Btu/hour x 0.293 071
Btu/minute x 17.584 267
Btu/second x 1055.056
calories/hour x 0.001 163 #
calories/minute x 0.069 78 #
calories/second x 4.1868 #
ft lbforce/minute x 0.022 597
ft lbforce/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
kgforce metres/hour x 0.002 724
kgforce metres/minute x 0.163 444
kilowatts [kW] x 1000 #
megawatts [MW] x 1 000 000 #
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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 is rarely
matched in the real world, though the error is small.
Call up a
Conversion Calculator for
Units
of Pressure OR the Background Notes on
Pressure
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
kgforce/sq.centimetre x 98 066.5 #
kgforce/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 #
poundsforce/sq.foot x 47.880
poundsforce/sq.inch x 6894.757
poundals/sq.foot x 1.448 16
tons(UK)force/sq.foot x 107 252
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
tonnesforce/sq.cm x 98 066 500 #
tonnesforce/sq.metre x 9806.65 #
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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.
Call up a Conversion
Calculator for
Units
of Speed OR the Background Notes on
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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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.
Call up a
Conversion Calculator for
Units
of Spread Rate OR the Background Notes on
Spread Rate
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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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.
Call up a
Conversion Calculator for
Units
of Spread Rate OR the Background Notes on
Spread Rate
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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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.
Call up a Conversion
Calculator for
Units of
Torque OR the Background Notes on
Torque
dyne centimetres divide by 10 000 000 #
gramforce centimetres x 0.000 098 066 5 #
kgforce centimetres x 0.098 066 5 #
kgforce metres x 9.806 65 #
newton centimetres divide by 100 #
newton metres [Nm] 1
ounceforce inches divide by 141.612
poundforce inches x 0.112 984
poundforce 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
tonneforce metres x 9 806.65 #
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Conversion Tables of Units for Science and Engineering
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.
The Dent Dictionary of Measurement
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.
The Economist Desk Companion
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 Encyclopaedia Britannica
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.
World Weights and Measures
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.
British Weights and Measures
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 preImperial units, a long list of premetric measures
used in Europe together with their British and metric
equivalents, and nearly 40 pages giving other sources.
The World of Measurements
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.
Scientific Unit Conversion
by Francois Cardarelli
SpringerVerlag, London, 1997 (456 pages)
ISBN 3540760229
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 (= handysized)
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.

There are now several
sites concerned with this topic. (It is popular with those wishing
to start up a site.) Almost all the Search Engines will find links
to more sites than anyone could really need, and each of those
will give more links . . . . .
The problem is simply: which one best suits the purpose?
The first to be considered
must the
Official SI Website in France.
In the UK
a very good place to make a start is the
Metrication Resource Site
run by Chris Keenan.
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.
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 86page book on the subject (SP 811)
which can be read online or downloaded and printed out  but note
that Adobe Acrobat Reader is needed.
The US Metric
Association is also a good starting point which provides a
wealth of links to other suitable sites.
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 (AngloSaxon, Biblical etc.) is provided by
Jack Proot
(in Canada)
The
International Standards
Organisation] [I S O] based in Switzerland, is responsible
for the worldwide 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.
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 Errors
 Whilst every care has been taken in the compilation of
this document, and many checks have been carried out, the
possibility of an error is always present in a work like
this and that must be borne in mind by all users. The author
would be glad to be told of any errors detected.
 Accuracy
 In a general dictionary like this it is impossible to
know just what accuracy is needed by any particular user.
Where the given value is an exact one then it has
been signalled. In most cases other values are accurate to
at least the number of significant figures shown. In some
cases it might be more than that as trailing zeros have not
been included.
 Presentation
 The conversion factors have mainly been presented as
multipliers, but exceptions to that have been made for two
reasons. First, it is easier to convey the exact value
'divide by 60' rather than the approximation 'multiply by
0.0166667' and it is more likely to be keyed in without
errors if a calculator is being used. Second, most
calculators accept only 8 digits, which means that 'multiply
by 0.000 084 666' will become '0.000 0846' (3 significant
figures) whereas 'divide by 11 811' will give the result to
6 significant figures. The appearance of a '1' needs no
operator but shows that the named unit is exactly equivalent
to the standard unit.


 Inverse usage
 In nearly all cases the conversion factors have been
given to change 'nonstandard' units into standard units of
the SI. For those cases where it is necessary to do a
conversion the other way it is only a matter of reversing
the operation. For example to convert feet into metres you
multiply by 0.3048 so, to convert metres into feet
you divide by 0.3048. Following on from this it can
be seen how conversions can be made between nonstandard
units, changing first into the standard unit and then back
into the required unit.
 Author's Note
 A guiding principle behind the writing and presentation
of this document has been that of clarity for
nonspecialist readers. To that end I have been guilty of
breaking "the rules" in a few places. I am sorry that these
transgressions may offend some readers but I have done so in
the belief that it will be a little bit easier for many, and
also help the flow of a continuous narrative.
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 online 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.

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For more information, visit
C I M T Home Page.
Publishing history
19th June 1995 (First placed online)
27th August 1997 (Minor corrections)
21st November 1997 (Major corrections and alterations)
20th January 1999 (Minor corrections and alterations)
9th August 1999 (A few adjustments to links)
13th December 1999 (Summary table of conversion factors added)
1st March 2000 (Some rewriting of Web section and links to first
conversion calculators put in)
1st May 2001 (Link to 'FAQ and other measures' put in)
2nd December 2001 (Several minor alterations throughout and 2
corrections made)
18th March 2002 (More links added)