Units

Quantity Unit Symbol
Acidity/alkalinity pH pH
Area hectare ha
  square kilometres km2 
Electrical conductance microsemens per centimetre µS/cm
Length micrometre µm
  millimetre mm
  centimetre cm
  metre m
  kilometre km
Mass microgram µg
  kilogram kg
  tonne t
  megatonne Mt
  gigatonne Gt
Power megawatt MW
  kilowatt-hour kWh
  gigawatt-hour GWh
Time second s
  hour hr
  day d
  year y
Velocity and speed kilometres per hour  km/hr
  metres per second m/s
Volume cubic metre m3 
Volume (fluids) litre L
  kilolitre kL
  megalitre ML
  gigalitres GL
  gigalitres per year GL/y
Work and energy petajoule PJ
Other abbreviations carbon dioxide equivalent units CO2-e
  parts per million ppm
  micrograms per cubic metre µg/m

Prefixes for SI units

Fraction Prefix Symbol
10–6 micro µ 
103 kilo k
106 mega M
109 giga G
106 peta P