Prefixes - multiples and sub-multiples of a unit - simply the use of large and small quantities. One thousand metres is simply one kilometre, and one-thousandth of a metre is one millimetre. Symbols for the prefixes are used with the abbreviations for the units, so one kilometre is 1km and one millimetre is 1mm.
| Prefix | Symbol | Meaning | Factor by which unit is multiplied | |
|---|---|---|---|---|
| tera | T | one million million | 1012 | 1,000,000,000,000 |
| giga | G | one thousand million | 109 | 1,000,000,000 |
| mega | M | one million | 106 | 1,000,000 |
| kilo | k | one thousand | 103 | 1,000 |
| hecto | h | one hundred | 102 | 100 |
| deka | d | ten | 10 | 10 |
| deci | d | one-tenth | 10-1 | 0.1 |
| centi | c | one-hundredth | 10-2 | 0.01 |
| milli | m | one-thousandth | 10-3 | 0.001 |
| micro | µ | one-millionth | 10-6 | 0.000,001 |
| nano | n | one-thousand millionth | 10-9 | 0.000,000,001 |
| pico | p | one-million millionth | 10-12 | 0.000,000,000,001 |