SI Prefixes
All 24 SI prefixes from quetta down to quecto, with symbol and power of ten. The four outermost — ronna, quetta, ronto, quecto — were added by the General Conference on Weights and Measures in 2022.
24 rows
| Prefix | Symbol | Factor | In digits |
|---|---|---|---|
| quetta | Q | 10³⁰ | — |
| ronna | R | 10²⁷ | — |
| yotta | Y | 10²⁴ | — |
| zetta | Z | 10²¹ | — |
| exa | E | 10¹⁸ | — |
| peta | P | 10¹⁵ | — |
| tera | T | 10¹² | — |
| giga | G | 10⁹ | 1000000000 |
| mega | M | 10⁶ | 1000000 |
| kilo | k | 10³ | 1000 |
| hecto | h | 10² | 100 |
| deca | da | 10¹ | 10 |
| deci | d | 10⁻¹ | 0.1 |
| centi | c | 10⁻² | 0.01 |
| milli | m | 10⁻³ | 0.001 |
| micro | µ | 10⁻⁶ | 0.000001 |
| nano | n | 10⁻⁹ | 0.000000001 |
| 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 | — |
A definition, not a calculation
Which name belongs to which exponent is fixed by the General Conference on Weights and Measures, so this column is quoted from the standard rather than derived. The digit column is computed from the exponent.
Questions
Why is the kilogram symbol kg and not Kg?
Prefix symbols are case-sensitive: k is kilo, K is the kelvin. Capital letters are reserved for prefixes from mega upwards and for unit symbols named after people.
What are ronna and quetta?
They are the newest prefixes, 10²⁷ and 10³⁰, adopted in 2022 together with ronto and quecto at the small end. The push came from data storage, where yotta was running out.
Can I stack two prefixes?
No. A millimicrometre is not a valid unit; write nanometre instead. The kilogram is the only apparent exception, and only because the base unit already carries a prefix in its name.
Sources and last check
Information, not professional advice.