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.
SI derived units
| Unit name | Symbol | Definition and what is measured |
| square metre | m2 |
Area
|
| cubic metre | m3 |
Volume
|
| metre per second | m/s | Speed or velocity |
| metre per second squared | m/s2 |
Acceleration
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
|
| kilogram per cubic metre | kg/m3 | Density |
SI derived units with special names and symbols
| Unit name | Symbol | Definition and what is measured |
| newton | N |
Force
The force which will accelerate a mass of 1 kg at a rate of 1 m/s2
|
| pascal | Pa |
Pressure = 1 N/m2
|
| joule | J |
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.
|
| watt | W |
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.
|
| degree Celsius | °C |
Temperature
0 °C = 273.15 K
Based on the temperatures at which water freezes (0 °C) and boils (100 °C at normal atmospheric pressure)
As used in weather forecasts, heating thermostats and ovens, etc.
|
| hertz | Hz |
Frequency (same as cycle/second)
The unit used for such things as radio channels, sound (pitch), and computer processor speed.
|
UK Metric Association 