# Derived units

These are derived from the base units as some meaningful combination. Some have special names whereas others are known by the elements that make them up and their mathematical relationship. Only a select few are listed here.

The unit names are only shown where applicable.

Derived units
Symbol Unit name What it measures
m2
Area (square metre)
See the list of approved units for others.
m3
Volume (cubic metre)
See the list of approved units for others.
m/s   Speed or velocity (metre per second)
m/s2
Acceleration (metre/(second squared))
Rate of change of speed (can be increasing or decreasing) e.g. if a moving object increases its speed by 1 m/s for every second of time that passes, then it is accelerating at the rate of 1 m/s2
kg/m3   Density (kilogram per cubic metre)
N newton
Force.
The force which will accelerate a mass of 1 kg at a rate of 1 m/s2
Pa pascal
Pressure = 1 N/m2
See list of approved units for others.
J joule
Energy
The energy required to accelerate a mass of 1 kg at a rate of 1 m/s2 over a distance of a metre (= 1 N m) Also tied to electrical units (see below). The kJ is the same as that used in nutrition data.
W watt
Power
Rate of expenditure of energy equal to 1 joule/second (J/s)
The familiar unit used with electrical appliances, but note the mechanical origin.
°C Celsius
Temperature
0 °C = 273.15 K
Based the temperatures at which water freezes (0 °C) and boils (100 °C at normal atmospheric pressure)
The same as used in weather forecasts and oven temperatures, etc.
Hz hertz
Frequency (same as cycle/second)
The unit used for such things as radio channels, sound (pitch) and computer processors (clock speed where 1 'tick' is a cycle).