THE INTERNATIONAL SYSTEM OF UNITS
The International System of Units, or SI (from the French Système international d’unités), is the modern revision of the metric system. It is the world’s most widely used system of measurement, both in everyday commerce and in science. Using the same standards of measurement makes it easier for scientists to communicate with one another. The SI is an evolving system; it can be modified through international agreement as the technology and precision of measurement progress and improve.
The SI consists of seven fundamental units: kilogram, meter, candela, second, ampere, kelvin, and mole – each representing different kinds of physical quantities – with a number of other derived units. The SI allows easy multiplication when switching among units having the same base but different prefixes to form decimal multiples or submultiples, that is smaller or larger quantities.
SI Base Units
| PHYSICAL QUANTITY | QUANTITY SYMBOL | BASIC SI UNIT NAME | UNIT SYMBOL |
|---|---|---|---|
| length | l, b, d, h, r, s, etc. | metre | m |
| mass | m | kilogram | kg |
| time | t | second | s |
| electric current | I | ampere | A |
| thermodynamic temperature | T | kelvin | K |
| amount of substance | n | mole | mol |
| luminous intensity | Iv | candela | cd |
SI Prefixes
| PREFIX | SYMBOL | LONG/SHORT SCALE (10N) | FACTOR OF BASE UNIT |
|---|---|---|---|
| giga- | G | Milliard / Billion | 10⁹ |
| mega- | M | Million | 10⁶ |
| kilo- | k | Thousand | 10³ |
| hecto- | h | Hundred | 10² |
| deka- | da | Ten | 10¹ |
| deci- | d | Tenth | 10⁻¹ |
| centi- | c | Hundredth | 10⁻² |
| milli- | m | Thousandth | 10⁻³ |
| micro- | µ | Millionth | 10⁻⁶ |
| nano- | n | Milliardth / Billionth | 10⁻⁹ |
| pico- | p | Billionth / Trillionth | 10⁻¹² |