Metric prefixes are a shorthand for powers of ten. A kilometer is a thousand meters, a milligram a thousandth of a gram, a nanosecond a billionth of a second. Because the same prefixes work on every SI unit, converting between them is always the same operation: move the decimal point. This converter does it exactly for all 24 official prefixes, works with any unit symbol you type, and shows the value with every prefix side by side.
How to use the metric prefix converter
- Enter the number in Value.
- Optionally type the base unit, such as m, g, L, W, Hz, F or B. It only labels the results.
- Choose the prefix you have in From prefix and the one you want in To prefix. “None” means the bare base unit.
- The tape shows the result, the power of ten you multiplied by and how many places the decimal point moved. The table lists the value with every prefix.
Metric prefix formula
Each prefix stands for 10 raised to an exponent. To convert, multiply by ten raised to the difference:
A positive difference moves the decimal point right (the number gets bigger, because the new unit is smaller); a negative difference moves it left. The converter shifts the decimal exponent directly rather than multiplying floating-point numbers, so results such as 0.1 µF → 100 nF come out exact.
Worked examples
Kilometers to millimeters: kilo = 10³, milli = 10⁻³. Difference: 3 − (−3) = 6. 2.5 km × 10⁶ = 2,500,000 mm.
Microfarads to nanofarads: micro = 10⁻⁶, nano = 10⁻⁹. Difference: 3. 4.7 µF × 10³ = 4,700 nF.
Megahertz to gigahertz: mega = 10⁶, giga = 10⁹. Difference: −3. 2,400 MHz × 10⁻³ = 2.4 GHz.
SI prefixes chart
| Prefix | Symbol | Power of ten | Multiplier |
|---|---|---|---|
| quetta | Q | 10³⁰ | nonillion |
| ronna | R | 10²⁷ | octillion |
| yotta | Y | 10²⁴ | septillion |
| zetta | Z | 10²¹ | sextillion |
| exa | E | 10¹⁸ | quintillion |
| peta | P | 10¹⁵ | quadrillion |
| tera | T | 10¹² | trillion |
| giga | G | 10⁹ | billion |
| mega | M | 10⁶ | million |
| kilo | k | 10³ | thousand |
| hecto | h | 10² | hundred |
| deca | da | 10¹ | ten |
| — | — | 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 | trillionth |
| femto | f | 10⁻¹⁵ | quadrillionth |
| atto | a | 10⁻¹⁸ | quintillionth |
| zepto | z | 10⁻²¹ | sextillionth |
| yocto | y | 10⁻²⁴ | septillionth |
| ronto | r | 10⁻²⁷ | octillionth |
| quecto | q | 10⁻³⁰ | nonillionth |
The number names use the US short scale, where a billion is 10⁹.
Rules for writing prefixes
- Case matters. M (mega, 10⁶) and m (milli, 10⁻³) differ by a factor of a billion; likewise P (peta) and p (pico).
- No space, no doubling. Write the prefix directly before the unit (km, µs) and never stack two prefixes; use ng, not mµg.
- The kilogram exception. The SI base unit of mass already contains a prefix, so prefixes are applied to the gram: a millionth of a kilogram is a milligram, not a microkilogram.
- Binary units are separate. In computing, KiB, MiB and GiB use powers of 1,024. See the data storage converter for those.
Where you will meet each range
Everyday life mostly uses kilo, centi and milli. Electronics lives between pico and mega (picofarads, microamps, megohms). Computing and telecom use giga and tera for storage and frequency. Chemistry and physics reach down to femtoseconds and nanometers, while astronomy and global energy statistics climb to exajoules and beyond. For numbers too large or small for any prefix, the scientific notation converter is the next step.
Frequently asked questions
How do I convert between metric prefixes?
Subtract the exponents and move the decimal point that many places. Kilo is 10³ and milli is 10⁻³, so going from kilo to milli moves the point 3 − (−3) = 6 places to the right: 2.5 km = 2,500,000 mm.
What are the newest metric prefixes?
In November 2022 the General Conference on Weights and Measures added ronna (R, 10²⁷), quetta (Q, 10³⁰), ronto (r, 10⁻²⁷) and quecto (q, 10⁻³⁰), the first new SI prefixes since 1991.
Why is micro written µ?
Micro uses the Greek letter mu (µ). When that character is unavailable, people often substitute a lowercase u, as in uF for microfarads, but µ is the official SI symbol.
Is deca abbreviated da or dk?
The SI symbol for deca (10¹) is da, as in dam for decameter. It is one of the few prefixes with a two-letter symbol and is rarely used outside of the dekagram in some European food labeling.