Cleave Books
A Dictionary of Units ~ Part 1
by Frank Tapson

This part provides a summary of most of the units of measurement to be found in use around the world today (and a few of historical interest), and the conversion factors needed to change them into a 'standard' unit of the SI.

A general account of systems of measurement is given in Part 2

  Here the units may be found either by looking under the 
in which they are used, (length energy etc.)  
 category  
  or by picking one unit from an alphabetically ordered   list of units.  
  There is a Summary Table of the most often required   Conversion Factors.  
  There are NO units of currency.  
Finally there are some   notes on this material .  


A separate document covers the most   FAQ and other measures.  

Or, to get a Conversion Calculator, select required category
from this table

Conversion Calculators
Any problems with any of these read the FAQ
Length Area Volume Mass Temperature
Feet & InchesAnglesPounds & Ounces

Units of Alcohol
Density Pressure
& Stress
Speed Fuel
Consumption
Power
or ONE calculator just for Changing Prefixes
Energy
(Work)
Flow Rate
by Mass        by Volume
Force Torque
Specific Energy
by Mass         by Volume
(Calorific Value)
Spread Rate
by Mass        by Volume
(including Rainfall)
Concentration
Line Density
(inc. Textiles)
Area Density Acceleration Viscosity
Dynamic        Kinematic
Specific Heat Capacity
by Mass        by Volume
Heat Flux
Density

Thermal
Conductivity

Thermal
Conductance
There is a Selection of Other Calculators also available


Summary table of conversion factors most often required
x means 'multiply by' . . . / means 'divide by' . . . # means it is an exact value
All other values given to an appropriate degree of accuracy.
To change . .into . .do this . . To change . .into . .do this . .
acreshectaresx 0.4047 kilogramsouncesx 35.3
acressq. kilometres/ 247 kilogramspoundsx 2.2046
acressq. metresx 4047 kilogramstonnes/ 1000 #
acressq. miles/ 640 # kilogramstons (UK/long)/ 1016
barrels (oil)cu.metres/ 6.29 kilogramstons (US/short)/ 907
barrels (oil)gallons (UK)x 34.97 kilometresmetresx 1000 #
barrels (oil)gallons (US)x 42 # kilometresmilesx 0.6214
barrels (oil)litresx 159 litrescu.inchesx 61.02
centimetresfeet/ 30.48 # litresgallons (UK)x 0.2200
centimetresinches/ 2.54 # litresgallons (US)x 0.2642
centimetresmetres/ 100 # litrespints (UK)x 1.760
centimetresmillimetresx 10 # litrespints (US liquid)x 2.113
cubic cmcubic inchesx 0.06102 metresyards/ 0.9144 #
cubic cmlitres/ 1000 # metrescentimetresx 100 #
cubic cmmillilitresx 1 # mileskilometresx 1.609
cubic feetcubic inchesx 1728 # millimetresinches/ 25.4 #
cubic feetcubic metresx 0.0283 ouncesgramsx 28.35
cubic feetcubic yards/ 27 # pints (UK)litresx 0.5683
cubic feetgallons (UK)x 6.229 pints (UK)pints (US liquid)x 1.201
cubic feetgallons (US)x 7.481 pints (US liquid)litresx 0.4732
cubic feetlitresx 28.32 pints (US liquid)pints (UK)x 0.8327
cubic inchescubic cmx 16.39 poundskilogramsx 0.4536
cubic incheslitresx 0.01639 poundsouncesx 16 #
cubic metrescubic feetx 35.31



To change . .into . .do this . . To change . .into . .do this . .




square cmsq. inchesx 0.1550
feetcentimetresx 30.48 # square feetsq. inchesx 144 #
feetmetresx 0.3048 # square feetsq. metresx 0.0929
feetyards/ 3 # square inchessquare cmx 6.4516 #
fl.ounces (UK)fl.ounces (US)x 0.961 square inchessquare feet/ 144 #
fl.ounces (UK)millilitresx 28.41 square kmacresx 247
fl.ounces (US)fl.ounces (UK)x 1.041 square kmhectaresx 100 #
fl.ounces (US)millilitresx 29.57 square kmsquare milesx 0.3861
gallonspintsx 8 # square metresacres/ 4047
gallons (UK)cubic feetx 0.1605 square metreshectares/ 10 000 #
gallons (UK)gallons (US)x 1.2009 square metresx 10.76
gallons (UK)litresx 4.54609 # square metressquare yardsx 1.196
gallons (US)cubic feetx 0.1337 square milesacresx 640 #
gallons (US)gallons (UK)x 0.8327 square mileshectaresx 259
gallons (US)litresx 3.785 square milessquare kmx 2.590
gramskilograms/ 1000 # square yardssquare metres/ 1.196
gramsounces/ 28.35 tonneskilogramsx 1000 #
hectaresacresx 2.471 tonnestons (UK/long)x 0.9842
hectaressquare km/ 100 # tonnestons (US/short)x 1.1023
hectaressquare metresx 10000 # tons (UK/long)kilogramsx 1016
hectaressquare miles/ 259 tons (UK/long)tonnesx 1.016
hectaressquare yardsx 11 960 tons (US/short)kilogramsx 907.2
inchescentimetresx 2.54 # tons (US/short)tonnesx 0.9072
inchesfeet/ 12 # yardsmetresx 0.9144 #
Go to
the top of this document

Categories of Units

length
area
volume or capacity
mass
temperature


density, area
density, line
density, volume
energy
force
fuel consumption
mass per unit length
mass per unit area
mass per unit volume


power
pressure
speed
spread rate (by mass)
spread rate (by volume)
stress
torque

Go to
the top of this document

List of Units

Units are listed in alphabetical order. 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
N - O - PQ - R - S - T - UVW - XYZ
A to K
A
acres
angstroms
ares
astronomical units
atmospheres
B
barleycorns
barrels (oil)
bars
British thermal units
Btu/hour etc.
bushels
C
calories
calories per hour etc.
carats, metric
Celsius
centigrade
centigrade heat units
centilitres
centimetres
centimetres of mercury or water
centimetres per minute etc.
chains (surveyors')
circular inches
cubic (+ any units)
cubic measures per area
cubits
D
decilitres
denier
drex
dynes
E
ells (UK)
ems (pica)
ergs (energy)
ergs (torque)
F
Fahrenheit
fathoms
feet
feet of water
feet per hour etc.
fluid ounces
foot pounds-force
foot pounds-force per minute etc.
foot poundals
furlongs
G
gallons
gallons per area
gigajoules
gigawatts
grains
grains per gallon
grams
gram-force centimetres
grams per area
grams per cm
grams per (any volume)
H
hands
hectares
hides
horsepower
horsepower hours
hundredweights
IJ
inches
inches of mercury or water
inches of rain (by mass)
inches of rain (by volume)
inches per minute etc.
joules
joules per hour etc.
K
Kelvin
kilocalories
kilocalories per hour etc.
kilograms-force
kilogram-force metres (energy)
kilogram-force metres (torque)
kilogram-force metres per hour etc.
kilogram-force per area
kilograms
kilograms per area
kilograms per metre
kilograms per volume
kilojoules
kilojoules per hour etc.
kilometres
kilometres per hour etc.
kilometres per litre
kilonewton per square metre
kilonewtons
kilopascals
kilowatts
kilowatt hours
kips (force)
kips per square inch
knots
L to Z
L
leagues
light years
links (surveyors')
litres
litres per area
M
Mach number
megajoules
meganewtons
meganewtons per square metre
megawatts
metres

metres of water
metres per second etc.
microns (=micrometres)
miles
miles per gallon
miles per hour etc.
millibars
milligrams per cm
milligrams per (any volume)
millilitres
millimetres of mercury or water
millimetres of rain (by mass)
millimetres of rain (by volume)
N
newton metres (energy)
newton metres (torque)
newtons (per area)
newtons (force)
newtons (weight)
O
ounces
ounces per inch
ounces per area
ounces per volume
PQ
parsecs
pascals
perch (=rods or poles)
picas
pints
points (printers')
poundals
poundals per square foot
pounds
pounds per area
pounds per foot
pounds per volume
pounds-force
pound-force inches
pounds-force per area
quarts
R
Rankine
Reaumur
roods
S
slugs (or g-pounds)
stones
square (+ any units)
squares (of timber)
sthenes
T
tex
therms
tonnes
ton-force metres
tonnes-force
tonnes-force per area
tonnes per hectare
tonnes per km
tonnes per volume
ton-force feet
tons
tons-force
tons-force per area
tons per acre
tons per mile
tons per volume
townships
troy ounce
UVW
watt second
watt hours
watts
XYZ
yards
yards per hour etc.
Go to
the top of this document

Length

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.
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.

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 #
Call up a Conversion Calculator for
Units of Length
OR the Background Notes on Length
Go to the top of this document

Area

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. 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.

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
Call up a Conversion Calculator for
Units of Area
OR the Background Notes on Area
Go to the top of this document

Volume or Capacity

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. When the metric system was introduced in the 1790's the litre was intended to match up with the volume occupied by 1 kilogram of pure water at a specified pressure and temperature. As the ability to measure things got better (by 100 years later) they found that there was a mismatch between the kilogram and the litre. As a result of this they had to redefine the litre (in 1901) as being 1.000028 cubic decimetres. Very handy!
This nonsense was stopped in 1964 when it was ruled that the word "litre" may be employed as a special name for the cubic decimetre, with the additional recommendation that for really accurate work, to avoid any possible confusion, the litre should not be used.
Here the litre is taken 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 #
Call up a Conversion Calculator for
Units of Volume
OR the Background Notes on Volume
Go to the top of this document

Mass (or Weight)

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.

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 #
Call up a Conversion Calculator for
Units of Mass
OR the Background Notes on Mass
Go to the top of this document

Temperature

There have been five main temperature scales, each one being named after the person who invented it.
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 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 (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)
Call up a Conversion Calculator for
Units of Temperature
OR the Background Notes on Temperature
Go to the top of this document

Line density

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.

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
Call up a Conversion Calculator for
Units of Line Density OR for Units of Textile (Yarn) Density
OR Background Notes on BOTH
Go to the top of this document

Density

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.

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
Call up a Conversion Calculator for
Units of Density
OR the Background Notes on Density
Go to the top of this document

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)
thermochemical calorie = cal(th)
mean calorie = cal(mean)
15 degree C calorie = cal(15C)
20 degree C calorie = cal(20C).
Unless a clear statement is made saying otherwise, assume the IT calorie is being used.
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.
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 pounds-force	 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 #
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 #
Call up a Conversion Calculator for
Units of Energy
OR the Background Notes on Energy
Go to the top of this document

Force

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.

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
Call up a Conversion Calculator for
Units of Force
OR the Background Notes on Force
Go to the top of this document

Fuel Consumption

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.
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
Call up a Conversion Calculator for
Units of Fuel Consumption
OR the Background Notes on Fuel Consumption
Go to the top of this document

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.
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 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 #
Call up a Conversion Calculator for Units of Power
OR the Background Notes on Power
Go to the top of this document

Pressure or Stress

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.

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 107 252
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
tonnes-force/sq.cm	x 98 066 500 #
tonnes-force/sq.metre	x 9806.65 #
Call up a Conversion Calculator for
Units of Pressure
OR the Background Notes on Pressure
Go to the top of this document

Speed

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.

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 #
Call up a Conversion Calculator for
Units of Speed
OR the Background Notes on Speed
Go to the top of this document

Spread Rate (by mass)

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.

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
Call up a Conversion Calculator for
Units of Spread Rate (by Mass)
OR the Background Notes on Spread Rate
Go to the top of this document

Spread Rate (by volume)

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.

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
Call up a Conversion Calculator for
Units of Spread Rate (by Volume)
OR the Background Notes on Spread Rate
Go to the top of this document

Torque

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.

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 #
Call up a Conversion Calculator for
Units of Torque
OR the Background Notes on Torque
Go to the top of this document

Notes

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 'non-standard' 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 non-standard 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 non-specialist 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 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.

Please send queries and comments to

Go to the top of this document


Go to Cleave Books Home Page.
©Frank Tapson2004