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Units & prefixes
GCSE & A-level
Powers-of-ten prefixes, the SI base units and the derived units in terms of them — the easy marks in unit conversions and “show your working”. Flip on Test yourself to drill them.
The units and prefixes worth knowing cold.
Prefixes
| Prefix | Symbol | Multiplier |
|---|---|---|
| tera | T | 10¹² |
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| centi | c | 10⁻² |
| milli | m | 10⁻³ |
| micro | μ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
| pico | p | 10⁻¹² |
SI base units
| Quantity | Unit | Symbol |
|---|---|---|
| length | metre | m |
| mass | kilogram | kg |
| time | second | s |
| electric current | ampere | A |
| temperature | kelvin | K |
| amount of substance | mole | mol |
Common derived units
| Quantity | Unit | In base units |
|---|---|---|
| force | newton (N) | kg·m·s⁻² |
| energy / work | joule (J) | N·m = kg·m²·s⁻² |
| power | watt (W) | J·s⁻¹ |
| pressure | pascal (Pa) | N·m⁻² |
| charge | coulomb (C) | A·s |
| potential difference | volt (V) | J·C⁻¹ |
| resistance | ohm (Ω) | V·A⁻¹ |
| frequency | hertz (Hz) | s⁻¹ |
Prefixes are powers of ten
nano = 10⁻⁹, kilo = 10³ … practise switching between them and standard form.
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