Units, their meaning and application

500 Tonne x 500kg
500kgs x 500 kg


500 kgs x 500KG x
500 tonnes x 500 KG x
500ts x 500t
500 Ton 500 t x
500 TON x 500 tonne
Length Area
10 millimetres    = 1 centimetre 100mm         = 1cm2
10 centimetres   = 1 decimetre 10000cm2       = 1m2
10 decimetres    = 1 metre 100m2             = 1 are
10 metres          = 1 decametre 100 ares          = 1 hectare
10 decametres   = 1 hectometre 10000m2         = 1 hectare
10 hectometres  = 1 kilometre 100 hectares    = 1 km2
1000 metres      = 1 kilometre 1000000m2     = 1 km2
Volume Capacity
1000mm3         = 1cm3 10 millilitres      = 1 centilitre
1000cm3          = 1dm3 10 centilitres     = 1 decilitre
1000dm3          = 1m3 10 decilitres      = 1 litre
1 million cm3     = 1m3 1000 litres        = 1 metre3
1000 grams       = 1 kilogram
1000 kilograms = 1 tonne

Weight (old)

16 ounces (oz)      = 1 pound (Ib)
112 pounds (Ib)    = 1 hundredweight (cwt)


20 hundredweight  = 1 Ton


12 inches    = 1 foot 144 sq inches  = 1 sq foot
3 feet          = 1 yard 9 sq feet          = 1 sq yard
22 yards     = 1 chain 4840 sq yards  = 1 acre
10 chains    = 1 furlong 640 acres         = 1 sq mile
8 furlongs   = 1 mile  
5280 feet    = 1 mile  
1760 yards = 1 mile  
length millimetre mm
length centimetre cm







mass tonne t
weight (old) Ton Ton
weight (old) Hundred weight cwt
weight (old) pound Ib




electric current



thermodynamic temperature      



amount of substance



luminous intensity




square meter m2
volume cubic meter m3
speed, velocity meter per second m/s
acceleration meter per second squared   m/s2
wave number reciprocal meter m-1
mass density kilogram per cubic meter kg/m3
specific volume cubic meter per kilogram m3/kg
current density ampere per square meter A/m2
magnetic field strength   ampere per meter A/m
amount-of-substance concentration mole per cubic meter mol/m3
luminance candela per square meter cd/m2
mass fraction kilogram per kilogram, which may be represented by the number 1 kg/kg = 1
plane angle radian (a) rad   - mm-1 = 1 (b)
solid angle steradian (a) sr (c)   - m2m-2 = 1 (b)
frequency hertz Hz   - s-1
force newton N   - mkgs-2
pressure, stress pascal Pa N/m2 m-1kgs-2
energy, work, quantity of heat   joule J Nm m2kgs-2
power, radiant flux watt W J/s m2kgs-3
electric charge, quantity of electricity coulomb C   - sA
electric potential difference,
electromotive force
volt V W/A m2kgs-3A-1
capacitance farad F C/V m-2kg-1s4A2
electric resistance ohm Omega V/A m2kgs-3A-2
electric conductance siemens S A/V m-2kg-1s3A2
magnetic flux weber Wb Vs m2kgs-2A-1
magnetic flux density tesla T Wb/m2 kgs-2A-1
inductance henry H Wb/A m2kgs-2A-2
Celsius temperature degree Celsius C   - K
luminous flux lumen lm cdsr (c) m2m-2cd = cd
illuminance lux lx lm/m2 m2m-4cd = m-2cd
activity (of a radionuclide) becquerel Bq   - s-1
absorbed dose, specific energy (imparted), kerma gray Gy J/kg m2s-2
dose equivalent (d) sievert Sv J/kg m2s-2
catalytic activity katal kat s-1mol
dynamic viscosity pascal second Pas
moment of force newton meter Nm
surface tension newton per meter N/m
angular velocity radian per second rad/s
angular acceleration radian per second squared rad/s2
heat flux density, irradiance watt per square meter W/m2
heat capacity, entropy joule per kelvin J/K
specific heat capacity, specific entropy joule per kilogram kelvin J/(kgK)
specific energy joule per kilogram J/kg
thermal conductivity watt per meter kelvin W/(mK)
energy density joule per cubic meter J/m3
electric field strength volt per meter V/m
electric charge density coulomb per cubic meter C/m3
electric flux density coulomb per square meter C/m2
permittivity farad per meter F/m
permeability henry per meter H/m
molar energy joule per mole J/mol
molar entropy, molar heat capacity joule per mole kelvin J/(molK)
exposure (x and gamma rays) coulomb per kilogram C/kg
absorbed dose rate gray per second Gy/s
radiant intensity watt per steradian W/sr
radiance watt per square meter steradian W/(m2sr)
catalytic (activity) concentration katal per cubic meter kat/m3
minute (time) min 1min = 60s
hour h 1h = 60min = 3600s
day d 1d = 24h = 86 400s
degree (angle) 1 = ( pi/180)rad
minute (angle) ' 1' = (1/60) = (pi/10 800)rad
second (angle) '' 1'' = (1/60)' = (pi/648 000)rad
litre L 1L = 1 dm3 = 10-3 m3
metric ton (a) t 1t = 103kg
neper Np 1Np = 1
bel (b) B 1B = (1/2)ln 10Np (c)
electron volt (d) eV 1eV = 1.602 18 x 10-19 J, approximately
unified atomic mass unit (e) u 1u = 1.660 54 x 10-27 kg, approximately
astronomical unit (f) ua 1ua = 1.495 98 x 1011 m, approximately
Only units of the SI and those units recognized for use with the SI are used to express the values of quantities. Equivalent values in other units are given in parentheses following values in acceptable units only when deemed necessary for the intended audience. There is no space between the figure and the unit when abbreviated. A space is only included when the word is written in full.

ie 100kg - 100 kilograms -  50 Ton -  50 tonne   

Abbreviations such as sec, cc, or mps are avoided and only standard unit symbols, prefix symbols, unit names, and prefix names are used.
 proper: s or second; cm3 or cubic centimetre; m/s or meter per second
          improper: sec; cc; mps
Unit symbols are unaltered in the plural.
l = 75cm
l = 75cms
Unit symbols are not followed by a period unless at the end of a sentence.
The length of the bar is 75cm.
The bar is 75cm long.
The bar is 75cm. long.
& division
A space or half-high dot is used to signify the multiplication of units. A solidus (i.e., slash), horizontal line, or negative exponent is used to signify the division of units. The solidus must not be repeated on the same line unless parentheses are used.
The speed of sound is about 344 ms-1  (meters per second)
The decay rate of 113Cs is about 21 ms-1  (reciprocal milliseconds)
m/s,  ms-2,  mkg/(s3A),  mkgs-3A-1

m/s,  m s-2,  m kg/(s3 A),  m kg s-3 A-1
The speed of sound is about 344 ms-1  (reciprocal milliseconds)
The decay rate of 113Cs is about 21 ms-1  (meters per second)
m s,  m/s/s,  mkg/s3/A
Variables and quantity symbols are in italic type. Unit symbols are in roman type. Numbers should generally be written in roman type. These rules apply irrespective of the typeface used in the surrounding text.  
She exclaimed, "That dog weighs 10kg!"
t = 3s, where t is time and s is second
T = 22K, where T is thermodynamic temperature, and K is kelvin
He exclaimed, "That dog weighs 10 kg!
t = 3s, where t is time and s is second
T = 22K, where T is thermodynamic temperature, and K is kelvin
Superscripts and subscripts are in italic type if they represent variables, quantities, or running numbers. They are in roman type if they are descriptive.
subscript category typeface proper usage 
quantity italic cp, specific heat capacity at constant pressure
descriptive roman mp, mass of a proton
running number italic
The combinations of letters "ppm," "ppb," and "ppt," and the terms part per million, part per billion, and part per trillion, and the like, are not used to express the values of quantities.
 proper: 2.0 L/L; 2.0 x 10-6 V;
4.3 nm/m; 4.3 x 10-9 l;
7 ps/s; 7 x 10-12 t,
where V, l, and t are the quantity symbols for volume, length, and time.
improper: "ppm," "ppb," and "ppt," and the terms part per million, part per billion, and part per trillion, and the like
Unit symbols (or names) are not modified by the addition of subscripts or other information. The following forms, for example, are used instead.
proper: Vmax = 1000V
a mass fraction of 10%
improper: V= 1000 Vmax
10 % (m/m) or 10 % (by weight)
The symbol % is used to represent simply the number 0.01.
proper: l1 = l2(1 + 0.2 %), or
D = 0.2 %,
where D is defined by the relation D = (l1 - l2)/l2.
improper: the length l1 exceeds the length l2 by 0.2 %
& units
Information is not mixed with unit symbols or names.
proper: the water content is 20mL/kg
improper: 20mL H2O/ kg
20mL of water/ kg

Math notation

It is clear to which unit symbol a numerical value belongs and which mathematical operation applies to the value of a quantity.
proper: 35cm x 48cm
1MHz to 10MHz or (1 to 10) MHz
20C to 30C or (20 to 30) C
123g 2g or (123 2) g
70% 5% or (70 5) %
x (1 10 %) V
35 x 48 cm
1MHz-10 MHz or 1 to 10 MHz
20 C-30 C or 20 to 30 C
123 2g
70 5%
240V 10 % (one cannot add 240V and 10%)
& names

Unit symbols and unit names are not mixed and mathematical operations are not applied to unit names.
 proper: kg/m3, kg m-3, or kilogram per cubic meter
 improper: kilogram/m3, kg/cubic meter, kilogram/cubic meter, kg per m3, or kilogram per meter3.
Numerals &
Values of quantities are expressed in acceptable units using Arabic numerals and symbols for units.
proper: m = 5kg
the current was 15A
improper: m = five kilograms
m = five kg
the current was 15 amperes
There is no space between the numerical value and unit symbol, even when the value is used in an adjectival sense, even in the case of superscript units for plane angle.
proper: a 25kg sphere
an angle of 2 3'  4"
If the spelled-out name of a unit is used, the normal rules of English apply: "a roll of 35-millimeter film."
improper: a 25-kg sphere
an angle of 2 3 ' 4 "
The digits of numerical values having more than four digits on either side of the decimal marker are separated into groups of three using a thin, fixed space counting from both the left and right of the decimal marker. Commas are not used to separate digits into groups of three.
15 739.012 53
15,739.012 53
Equations between quantities are used in preference to equations between numerical values, and symbols representing numerical values are different from symbols representing the corresponding quantities. When a numerical-value equation is used, it is properly written and the corresponding quantity equation is given where possible.
 proper: (l/m) = 3.6-1 [v/(km/h)](t/s)
l = 3.6-1 vt, accompanied by text saying,
"where l is in meters, v is in kilometers per hour, and t is in seconds"
Standardized quantity symbols are used. Similarly, standardized mathematical signs and symbols are used. More specifically, the base of "log" in equations is specified when required by writing loga x (meaning log to the base aof x), lb x (meaning log2 x), ln x (meaning loge x), or lg x (meaning log10 x).
proper: tan x
R for resistance
r for relative atomic mass
improper: tg x for tangent of x
words, acronyms, or ad hoc groups of letters
Weight vs.
When the word "weight" is used, the intended meaning is clear. (In science and technology, weight is a force, for which the SI unit is the Newton; in commerce and everyday use, weight is usually a synonym for mass, for which the SI unit is the kilogram.)
A quotient quantity is written explicitly.
proper: mass divided by volume
improper: mass per unit volume
Object &
An object and any quantity describing the object are distinguished. (Note the difference between "surface" and "area," "body" and "mass," "resistor" and "resistance," "coil" and "inductance.")
proper: A body of mass 5g
improper: A mass of 5g