Computed, not transcribed
The prefix names, symbols and exponents are taken verbatim from the SI Brochure; the decimal column is the exponent expanded programmatically, so it can not drift from the power of ten beside it.
SI Unit Prefixes
All 24 SI prefixes from quecto (10⁻³⁰) to quetta (10³⁰) with symbol, power of ten and decimal value — including the four added in 2022.
Prefixes
24
Largest
10³⁰ (Q)
Smallest
10⁻³⁰ (q)
Last added
2022
The SI defines 24 prefixes, from quetta (10³⁰) down to quecto (10⁻³⁰). Kilo means 10³, milli means 10⁻³.
Verified
SI Unit Prefixes — in full
24 of 24 rows
| Prefix | Symbol | Factor | Decimal | Example | Group |
|---|---|---|---|---|---|
| quetta | Q | 10³⁰ | 1,000,000,000,000,000,000,000,000,000,000 | 1 QB = 10³⁰ bytes | Multiplying |
| ronna | R | 10²⁷ | 1,000,000,000,000,000,000,000,000,000 | Earth's mass ≈ 6 Rg | Multiplying |
| yotta | Y | 10²⁴ | 1,000,000,000,000,000,000,000,000 | 1 YB = 10²⁴ bytes | Multiplying |
| zetta | Z | 10²¹ | 1,000,000,000,000,000,000,000 | Global data volume is measured in ZB | Multiplying |
| exa | E | 10¹⁸ | 1,000,000,000,000,000,000 | Exascale computing: 10¹⁸ operations per second | Multiplying |
| peta | P | 10¹⁵ | 1,000,000,000,000,000 | 1 PB = 1,000 TB | Multiplying |
| tera | T | 10¹² | 1,000,000,000,000 | A 2 TB hard drive | Multiplying |
| giga | G | 10⁹ | 1,000,000,000 | A 3 GHz processor | Multiplying |
| mega | M | 10⁶ | 1,000,000 | 1 MW powers ~1,000 homes | Multiplying |
| kilo | k | 10³ | 1,000 | 1 km = 1,000 m | Multiplying |
| hecto | h | 10² | 100 | 1 hPa = 100 Pa (air pressure) | Multiplying |
| deca | da | 10¹ | 10 | 1 dag = 10 g | Multiplying |
| deci | d | 10⁻¹ | 0.1 | 1 dl = 0.1 l | Dividing |
| centi | c | 10⁻² | 0.01 | 1 cm = 0.01 m | Dividing |
| milli | m | 10⁻³ | 0.001 | 1 mm = 0.001 m | Dividing |
| micro | µ | 10⁻⁶ | 0.000001 | 1 µm — the scale of a bacterium | Dividing |
| nano | n | 10⁻⁹ | 0.000000001 | 1 nm — chip manufacturing scale | Dividing |
| pico | p | 10⁻¹² | 0.000000000001 | 1 pF — capacitor ratings | Dividing |
| femto | f | 10⁻¹⁵ | 0.000000000000001 | 1 fm — the size of a nucleus | Dividing |
| atto | a | 10⁻¹⁸ | 0.000000000000000001 | 1 as — attosecond laser pulses | Dividing |
| zepto | z | 10⁻²¹ | 0.000000000000000000001 | 1 zg — mass of a few atoms | Dividing |
| yocto | y | 10⁻²⁴ | 0.000000000000000000000001 | 1 yg — below a single proton mass | Dividing |
| ronto | r | 10⁻²⁷ | 0.000000000000000000000000001 | Electron mass ≈ 0.9 rg | Dividing |
| quecto | q | 10⁻³⁰ | 0.000000000000000000000000000001 | 1 qs — smaller than any measured interval | Dividing |
How to read this table
A prefix stands in for a power of ten in front of the unit: 1 km is 10³ m, 1 µs is 10⁻⁶ s. The “Decimal” column writes that same factor out in full.
Watch the case. A capital M means mega (10⁶), a lower-case m means milli (10⁻³) — nine powers of ten apart.
Prefixes are never stacked: there is no “millimicrometre”. For 10⁻⁹ m you use the nanometre.
The exponent ladder
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The ladder rises in steps of three — except in the middle, where hecto, deca, deci and centi insert single steps.
Step between neighbouring prefixes
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18 of the 23 transitions are steps of three. The four exceptions predate standardisation and survived out of habit.
Prefixes per magnitude band
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Prefixes cluster around unity, where everyday measurement happens. Further out the ladder becomes uniformly coarse.
How this table is built
Sources & verification
Last checked against the sources on August 6, 2026.
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Frequently asked questions
How many SI prefixes are there?
- The four newest — ronna, quetta, ronto and quecto — were adopted at the General Conference on Weights and Measures in 2022.
Why were new prefixes added in 2022?
Because data volumes and astronomical masses had outgrown yotta. Without new prefixes, unofficial names would have taken hold — the addition got ahead of them.
Why does the case of the symbol matter?
Because it changes the meaning: M is mega (10⁶), m is milli (10⁻³). As a rule capitals from mega upward are multiplying prefixes and lower-case letters are dividing ones — with k for kilo as the best-known exception.
Do these prefixes apply to data sizes as well?
Officially yes: 1 kB is 1,000 bytes. Powers of two have their own IEC prefixes Ki, Mi, Gi — 1 KiB is 1,024 bytes. Operating systems and drive manufacturers still use different conventions.
Why do hecto, deca, deci and centi break the steps of three?
They come from the original metric system of 1795, which did not yet use steps of three. In practice mainly the centimetre and the hectopascal survived.
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