With scientific research going all over the world, the communication is very important. This communication becomes very easy if there is an agreement on international level regarding the use of single set of symbols and units for the physical quantities being used. So with the same motive, scientists have used a number of such systems of units in past, International System of units being the latest one. In the 11th Conference on Weights and Measures, some major changes were proposed in the metric system of units and a new name was given; International system of units.
There are basic seven types of units at core level listed below: –
| Physical Quantity | Symbol | SI Unit | Abbreviation |
| Length | l | metre | m |
| Mass | m | Kilogram | kg |
| Time | t | second | s |
| Electric current | I | ampere | A |
| Luminous intensity | lv | candela | cd |
| Amount of substance (moles) | n | mole | mol |
Rest of the units are derived from these basic units only. For example: – the basic unit of length is ‘m’ and units of metric area are m2 and of metric volume is m3 .
