This is a searchable reference of all SI (metric) prefixes, from quetta (10³⁰) down to quecto (10⁻³⁰), including the everyday ones (kilo, mega, giga, milli, micro, nano) and the 2022 BIPM additions. It is for students, engineers and anyone decoding a unit symbol.
How it works
Each SI prefix is a fixed power of ten that multiplies the base unit. To apply a prefix, multiply by its factor; to remove it, divide. The table lists the prefix name, its symbol, the power of ten, the full numeric factor, and the short-scale name (thousand, million, billion). Type in the search box to filter by name, symbol or scale.
Case matters. Capital M is mega (a million) while lowercase m is milli (a thousandth). The difference is 10⁹ — a billion-fold error — so always check the symbol capitalization when reading a unit.
The full set
| Prefix | Symbol | Power | Factor |
|---|---|---|---|
| quetta | Q | 10³⁰ | 1,000,000,000,000,000,000,000,000,000,000 |
| ronna | R | 10²⁷ | — |
| yotta | Y | 10²⁴ | — |
| zetta | Z | 10²¹ | — |
| exa | E | 10¹⁸ | — |
| peta | P | 10¹⁵ | — |
| tera | T | 10¹² | trillion |
| giga | G | 10⁹ | billion |
| mega | M | 10⁶ | million |
| kilo | k | 10³ | thousand |
| hecto | h | 10² | hundred |
| deca | da | 10¹ | ten |
| (none) | — | 10⁰ | one |
| deci | d | 10⁻¹ | tenth |
| centi | c | 10⁻² | hundredth |
| milli | m | 10⁻³ | thousandth |
| micro | µ | 10⁻⁶ | millionth |
| nano | n | 10⁻⁹ | billionth |
| pico | p | 10⁻¹² | — |
| femto | f | 10⁻¹⁵ | — |
| atto | a | 10⁻¹⁸ | — |
| zepto | z | 10⁻²¹ | — |
| yocto | y | 10⁻²⁴ | — |
| ronto | r | 10⁻²⁷ | — |
| quecto | q | 10⁻³⁰ | — |
Common conversions using prefixes
To convert 5 GW (gigawatts) to watts, apply giga = 10⁹:
5 × 1,000,000,000 = 5,000,000,000 W.
To convert 2.5 µs (microseconds) to seconds, apply micro = 10⁻⁶:
2.5 × 0.000001 = 0.0000025 s.
The 2022 additions: ronna, quetta, ronto, quecto
The BIPM (International Bureau of Weights and Measures) added four new prefixes in November 2022, extending the range from ±24 powers to ±30. They were needed because datasets in astronomy, particle physics, and data storage were reaching scales that had no official SI name. A ronnabyte (10²⁷ bytes) and a quettabyte (10³⁰ bytes) are now formally defined, even if no storage device comes close to them yet.
Practical notes
- The micro symbol µ (U+00B5) is sometimes typed as the ASCII letter u in plain text. Both are accepted conventions, but µ is the correct SI symbol.
- Kilo uses lowercase k, not capital K.
KHzis technically wrong;kHzis correct. - Prefixes are always attached directly to the unit symbol with no space:
km,mL,GHz— notk morG Hz. - The prefixes
hecto,deca,deci, andcenti(h, da, d, c) are not used in physics but appear regularly in everyday units such as cm (centimetre), dL (decilitre), and hPa (hectopascal, used in weather reports).