SI Prefix Reference
From quetta (Q, 10³⁰) down to quecto (q, 10⁻³⁰).
Overview
The SI Prefix Reference lists every metric prefix defined by the International Bureau of Weights and Measures, from quetta (10³⁰) down to quecto (10⁻³⁰). Each row shows the prefix name, its symbol, the power of ten it represents and an example unit (megajoule, micrometre, nanofarad) that makes the magnitude concrete.
It is built for engineers and scientists translating between giga and tera in spec sheets, students checking unit conversions and anyone who's wondered whether "quetta" is really a thing. Long-tail queries it covers include "what comes after yotta SI prefix", "SI prefix for 10^-9", "milli vs micro vs nano" and "official SI prefixes list 2022".
How it works
The 2022 revision of the SI added four new prefixes — ronna (R, 10²⁷), quetta (Q, 10³⁰), ronto (r, 10⁻²⁷) and quecto (q, 10⁻³⁰) — extending the range past what the previous yotta / yocto limit allowed. The reference includes all 24 official prefixes, paired into positive and negative powers.
Each row shows the name, the official symbol (case matters: M is mega, m is milli), the multiplier as a power of ten and a worked example. The table is sorted from largest to smallest. The lookup also makes clear that the prefixes follow strict powers of 1000 above kilo and below milli, but use 10 and 100 between them (deca, hecto, deci, centi).
Examples
quetta → Q → 10³⁰
mega → M → 10⁶ → 1 MJ ≈ a stick of dynamite
nano → n → 10⁻⁹ → 1 nm ≈ a glucose molecule
quecto → q → 10⁻³⁰
FAQ
Why were ronna and quetta added in 2022?
Data storage was about to overflow yotta, which had been the top prefix since 1991. The conference adopted ronna (10²⁷) and quetta (10³⁰) to give some headroom — and the matching small prefixes ronto and quecto for symmetry.
Is "tebibyte" an SI prefix?
No. Tebi (Ti) is from the IEC binary prefix family — 2⁴⁰, used for digital storage. SI prefixes are strictly powers of 10. A terabyte is 10¹² bytes; a tebibyte is 2⁴⁰ bytes, about 10% larger.
Why is the symbol for micro a Greek mu?
µ (the Greek letter mu) was chosen to avoid collision with "m" for milli. In ASCII-limited contexts, "u" is sometimes used (uF for microfarad), but the official symbol is µ.
Are the symbols case-sensitive?
Yes. M is mega and m is milli — a million times apart. Be careful in plain text. The only common ambiguity is k (kilo) vs K (kelvin), and even there only one is a prefix.
Are deca, hecto, deci and centi still used?
Officially yes, but mostly only in deciliter, centimeter and a handful of historical units (hectare = 100 are). Engineering tends to skip from kilo straight to milli.