Units, their meaning and application
500 Tonne  x  500kg  
500kgs  x  500 kg 
x 
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^{2 } = 1cm^{2}  
10 centimetres = 1 decimetre  10000cm^{2} = 1m^{2}  
10 decimetres = 1 metre  100m^{2} = 1 are  
10 metres = 1 decametre  100 ares = 1 hectare  
10 decametres = 1 hectometre  10000m^{2} = 1 hectare  
10 hectometres = 1 kilometre  100 hectares = 1 km^{2}  
1000 metres = 1 kilometre  1000000m^{2} = 1 km^{2}  
Volume  Capacity  
1000mm^{3} = 1cm^{3}  10 millilitres = 1 centilitre  
1000cm^{3} = 1dm^{3}  10 centilitres = 1 decilitre  
1000dm^{3} = 1m^{3}  10 decilitres = 1 litre  
1 million cm^{3} = 1m^{3}  1000 litres = 1 metre^{3}  
Mass  
1000 grams = 1 kilogram  
1000 kilograms = 1 tonne  
Weight (old) 

16 ounces (oz) = 1 pound (Ib)  
112 pounds (Ib) = 1 hundredweight (cwt)  
Length 
20 hundredweight = 1 Ton 
Area 
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  

area 
square meter  m^{2} 
volume  cubic meter  m^{3} 
speed, velocity  meter per second  m/s 
acceleration  meter per second squared  m/s^{2} 
wave number  reciprocal meter  m^{1} 
mass density  kilogram per cubic meter  kg/m^{3} 
specific volume  cubic meter per kilogram  m^{3}/kg 
current density  ampere per square meter  A/m^{2} 
magnetic field strength  ampere per meter  A/m 
amountofsubstance concentration  mole per cubic meter  mol/m^{3} 
luminance  candela per square meter  cd/m^{2} 
mass fraction  kilogram per kilogram, which may be represented by the number 1  kg/kg = 1 
plane angle  radian ^{(a)}  rad    m·m^{1 }= 1 ^{(b)} 
solid angle  steradian ^{(a)}  sr ^{(c)}    m^{2}·m^{2 }= 1 ^{(b)} 
frequency  hertz  Hz    s^{1} 
force  newton  N    m·kg·s^{2} 
pressure, stress  pascal  Pa  N/m^{2}  m^{1}·kg·s^{2} 
energy, work, quantity of heat  joule  J  N·m  m^{2}·kg·s^{2} 
power, radiant flux  watt  W  J/s  m^{2}·kg·s^{3} 
electric charge, quantity of electricity  coulomb  C    s·A 
electric potential difference, electromotive force 
volt  V  W/A  m^{2}·kg·s^{3}·A^{1} 
capacitance  farad  F  C/V  m^{2}·kg^{1}·s^{4}·A^{2} 
electric resistance  ohm  V/A  m^{2}·kg·s^{3}·A^{2}  
electric conductance  siemens  S  A/V  m^{2}·kg^{1}·s^{3}·A^{2} 
magnetic flux  weber  Wb  V·s  m^{2}·kg·s^{2}·A^{1} 
magnetic flux density  tesla  T  Wb/m^{2}  kg·s^{2}·A^{1} 
inductance  henry  H  Wb/A  m^{2}·kg·s^{2}·A^{2} 
Celsius temperature  degree Celsius  °C    K 
luminous flux  lumen  lm  cd·sr ^{(c)}  m^{2}·m^{2}·cd = cd 
illuminance  lux  lx  lm/m^{2}  m^{2}·m^{4}·cd = m^{2}·cd 
activity (of a radionuclide)  becquerel  Bq    s^{1} 
absorbed dose, specific energy (imparted), kerma  gray  Gy  J/kg  m^{2}·s^{2} 
dose equivalent ^{(d)}  sievert  Sv  J/kg  m^{2}·s^{2} 
catalytic activity  katal  kat  s^{1}·mol 
dynamic viscosity  pascal second  Pa·s 
moment of force  newton meter  N·m 
surface tension  newton per meter  N/m 
angular velocity  radian per second  rad/s 
angular acceleration  radian per second squared  rad/s^{2} 
heat flux density, irradiance  watt per square meter  W/m^{2} 
heat capacity, entropy  joule per kelvin  J/K 
specific heat capacity, specific entropy  joule per kilogram kelvin  J/(kg·K) 
specific energy  joule per kilogram  J/kg 
thermal conductivity  watt per meter kelvin  W/(m·K) 
energy density  joule per cubic meter  J/m^{3} 
electric field strength  volt per meter  V/m 
electric charge density  coulomb per cubic meter  C/m^{3} 
electric flux density  coulomb per square meter  C/m^{2} 
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/(mol·K) 
exposure (x and 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/(m^{2}·sr) 
catalytic (activity) concentration  katal per cubic meter  kat/m^{3} 
minute (time)  min  1min = 60s 
hour  h  1h = 60min = 3600s 
day  d  1d = 24h = 86 400s 
degree (angle)  °  1° = ( /180)rad 
minute (angle)  1 = (1/60)° = (/10 800)rad  
second (angle)  1 = (1/60) = (/648 000)rad  
litre  L  1L = 1 dm^{3 }= 10^{3} m^{3} 
metric ton ^{(a)}  t  1t = 10^{3}kg 
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 10^{11} m, approximately 
#1 General 
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 

#2 Abbreviations 
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; cm^{3} or cubic centimetre; m/s or meter per second  
improper:  sec; cc; mps  
#3 Plurals 
Unit symbols are unaltered in the plural.  
proper:

l = 75cm  
improper:

l = 75cms  
#4 Punctuation 
Unit symbols are not followed by a period unless at the end of a sentence.  
proper:

The length of the bar
is 75cm. The bar is 75cm long. 

improper:

The bar is 75cm. long.  
#5 Multiplication & division 
A space or halfhigh 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.  
^{ }proper:

The speed of sound is
about 344 m·s^{1} (meters per second)^{
}The decay rate of ^{113}Cs is about 21 ms^{1} (reciprocal
milliseconds) m/s, m·s^{2}, m·kg/(s^{3}·A), m·kg·s^{3}·A^{1} m/s, m s^{2}, m kg/(s^{3} A), m kg s^{3} A^{1} 

^{ }improper:

The speed of sound is
about 344 ms^{1} (reciprocal milliseconds)^{
}The decay rate of ^{113}Cs is about 21 m·s^{1} (meters
per second) m ÷ s, m/s/s, m·kg/s^{3}/A 

#6 Typeface 
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.  
proper:

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 

improper:

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 

#7 Typeface 
Superscripts and subscripts are in italic type if they represent variables, quantities, or running numbers. They are in roman type if they are descriptive.  


#8 Abbreviations 
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 µL/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  
#9 Unit modifications 
Unit symbols (or names) are not modified by the addition of subscripts or other information. The following forms, for example, are used instead.  
proper:  V_{max}
= 1000V a mass fraction of 10% 

improper:  V= 1000 V_{max }10 % (m/m) or 10 % (by weight) 
#10 Percent 
The symbol % is used to represent simply the number 0.01.  
proper:  l_{1}
= l_{2}(1 + 0.2 %), or D = 0.2 %, where D is defined by the relation D = (l_{1}  l_{2})/l_{2}. 

improper:  the length l_{1 }exceeds the length l_{2 }by 0.2 %  
#11 Information & units 
Information is not mixed with unit symbols or names.  
proper:  the water content is 20mL/kg  
improper:  20mL H_{2}O/
kg 20mL of water/ kg 

#12 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 20°C to 30°C or (20 to 30) °C 123g ± 2g or (123 ± 2) g 70% ± 5% or (70 ± 5) % 240 x (1 ± 10 %) V 

improper: 
35 x
48 cm 1MHz10 MHz or 1 to 10 MHz 20 °C30 °C or 20 to 30 °C 123 ± 2g 70 ± 5% 240V ± 10 % (one cannot add 240V and 10%) 

#13 Unit symbols & names 
Unit symbols and unit names are not mixed and mathematical operations are not applied to unit names.  
^{ }proper:  kg/m^{3}, kg · m^{3}, or kilogram per cubic meter  
^{ }improper:  kilogram/m^{3}, kg/cubic meter, kilogram/cubic meter, kg per m^{3}, or kilogram per meter^{3}.  
#14 Numerals & unit symbols 
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 

#15 Unit spacing 
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 spelledout name of a unit is used, the normal rules of English apply: "a roll of 35millimeter film." 

improper:  a 25kg sphere an angle of 2 ° 3 ' 4 " 

#16 Digit spacing 
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.  
proper:

15 739.012 53  
improper:

15739.01253 15,739.012 53 

#17 Quantity equations 
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 numericalvalue 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)  
^{ }improper:

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" 

#18 Standard symbols 
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 

proper:  tan x R for resistance A_{r} for relative atomic mass 

improper:  tg x for
tangent of x words, acronyms, or ad hoc groups of letters 

#19 Weight vs. mass 
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.)  
#20 Quotient quantity 
A quotient quantity is written explicitly.  
proper:  mass divided by volume  
improper:  mass per unit volume  
#21 Object & quantity 
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  