Metric (SI) Prefixes
Metric prefixes scale a unit by powers of ten. The same prefixes work with every SI unit: meters, grams, liters, watts, bytes and more.
Prefix table
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| quetta | Q | 10³⁰ | — |
| ronna | R | 10²⁷ | Earth’s mass ≈ 6 Rg |
| yotta | Y | 10²⁴ | — |
| zetta | Z | 10²¹ | global data ≈ hundreds of ZB |
| exa | E | 10¹⁸ | — |
| peta | P | 10¹⁵ | petabyte |
| tera | T | 10¹² | terabyte drive |
| giga | G | 10⁹ | gigahertz processor |
| mega | M | 10⁶ | megawatt |
| kilo | k | 10³ | kilometer, kilogram |
| hecto | h | 10² | hectopascal, hectare (hm²) |
| deca | da | 10¹ | decaliter |
| — | — | 10⁰ | base unit |
| deci | d | 10⁻¹ | deciliter |
| centi | c | 10⁻² | centimeter |
| milli | m | 10⁻³ | millimeter, milliliter |
| micro | µ | 10⁻⁶ | micrometer |
| nano | n | 10⁻⁹ | nanosecond |
| pico | p | 10⁻¹² | picofarad |
| femto | f | 10⁻¹⁵ | femtosecond laser |
| atto | a | 10⁻¹⁸ | — |
| zepto | z | 10⁻²¹ | — |
| yocto | y | 10⁻²⁴ | — |
| ronto | r | 10⁻²⁷ | — |
| quecto | q | 10⁻³⁰ | — |
Using prefixes
- Capitalisation matters: m is milli, M is mega; k (kilo) is always lower case.
- Never stack prefixes: write ns, not mµs.
- The kilogram is the only SI base unit that already contains a prefix, so multiples are formed from the gram: mg, g, kg, Mg.
- In computing, binary prefixes (Ki, Mi, Gi) mean powers of 1,024 — see data storage.