Metric Prefixes Explained
A complete guide to SI metric prefixes from quetta to quecto, with a full chart, symbols, powers of 10, and worked conversion examples.
Last updated: 2026-05-21
What Are Metric Prefixes?
A metric prefix is a short word attached to the front of a base unit that scales it by a power of 10. Instead of writing 1,000 meters, you write one kilometer; instead of 0.001 second, you write one millisecond. The prefix never changes what is being measured — it only changes the size of the step you count in.
This is the central advantage of the metric (SI) system: every prefix is a clean multiple of ten, so scaling up or down means moving a decimal point rather than memorizing arbitrary conversion factors. The same prefixes apply to every base unit, whether you are measuring length, mass, time, or data.
Each prefix has a name (such as kilo), a symbol (such as k), and a defining factor (such as 103, or 1,000). Learn the factor and you can read any combination instantly.
The Full SI Prefix Chart
The table below lists every official SI prefix, from the largest (quetta, 1030) down to the smallest (quecto, 10−30). The four outermost prefixes — ronna, quetta, ronto, and quecto — were adopted in 2022 to handle the scale of modern data and physics.
| Prefix | Symbol | Factor | Decimal |
|---|---|---|---|
| quetta | Q | 1030 | 1,000,000,000,000,000,000,000,000,000,000 |
| ronna | R | 1027 | 1,000,000,000,000,000,000,000,000,000 |
| yotta | Y | 1024 | 1,000,000,000,000,000,000,000,000 |
| zetta | Z | 1021 | 1,000,000,000,000,000,000,000 |
| exa | E | 1018 | 1,000,000,000,000,000,000 |
| peta | P | 1015 | 1,000,000,000,000,000 |
| tera | T | 1012 | 1,000,000,000,000 |
| giga | G | 109 | 1,000,000,000 |
| mega | M | 106 | 1,000,000 |
| kilo | k | 103 | 1,000 |
| hecto | h | 102 | 100 |
| deca | da | 101 | 10 |
| (base unit) | — | 100 | 1 |
| 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 | 0.000000000001 |
| femto | f | 10−15 | 0.000000000000001 |
| atto | a | 10−18 | 0.000000000000000001 |
| zepto | z | 10−21 | 0.000000000000000000001 |
| yocto | y | 10−24 | 0.000000000000000000000001 |
| ronto | r | 10−27 | 0.000000000000000000000000001 |
| quecto | q | 10−30 | 0.000000000000000000000000000001 |
Notice the symbol casing: prefixes of one million and larger take uppercase symbols (M, G, T, P), while smaller prefixes take lowercase (m, n, p). Kilo is the one historical exception — it stays lowercase as k.
Common Examples
You already use metric prefixes every day, often without naming them:
- Kilometer (km) — 1,000 meters. The standard unit for road distance in most of the world.
- Megabyte (MB) — one million bytes (in the decimal sense). A short song or a high-resolution photo.
- Milliliter (mL) — one thousandth of a liter. A teaspoon is about 5 mL.
- Microsecond (µs) — one millionth of a second. The timescale of fast electronics.
- Nanometer (nm) — one billionth of a meter. Used to measure wavelengths of light and chip features.
How to Convert Between Prefixes
To move from one prefix to another, subtract the target prefix's power of 10 from the source prefix's power of 10. The result tells you how many places to shift the decimal point — positive means shift right, negative means shift left.
Worked example: convert 3 kilometers to millimeters. Kilo is 103 and milli is 10−3. The difference is 3 − (−3) = 6, so shift the decimal 6 places to the right:
- Start: 3 km
- Shift 6 places right: 3 × 106 = 3,000,000
- Result: 3 km = 3,000,000 mm
The same rule works in reverse and across every base unit. When you need an exact figure without counting zeros by hand, run it through one of our all converters and the decimal shift is handled for you.