| THE SI SYSTEM | |||
| Physical Quantity | Unit | Symbol | Definition of Units |
| Length | Meter | m | |
| Mass | Kilogram | kg | |
| Time | Second | s | The basic units of the SI System |
| Electric current | Ampere | A | |
| Temperature | Kelvin | K | |
| Amount of substance | Mole | mol | |
| Energy | Joule | J | kg m2s-2 |
| Force | Newton | N | J m-1 |
| Electric charge | Coulomb | C | A s |
| Electric potential difference | Volt | V | J A-1s-1 |
| Electrical resistance | Ohm | Ω | V A -1 |
| Power | Watt | W | J s -1 |
| SOME WIDELY USED NON-SI UNITS | |||
| Physical Quantity | Unit | Symbol | Definition of Units |
| Length | Ångstrom | Å | 10-10m |
| Micron | µ | 10-6m | |
| Volume | Liter | 1 | 10-3m3 |
| Energy | Calorie | cal | 4.184J |
| Erg | erg | 10-7J | |
| Electronvolt | eV | 1.6021 x 10-19J | |
| Kilowatt hour | kWh | 3.6 x 106J | |
| Pressure | Atmosphere | atm | 1.01325 x 105N m-2 |
| Millimeter of mercury | mmHg | 133.322 N m-2 | |