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