How to use the SI prefix table and converter
- Type a Value. Plain numbers, E notation (4.5e-3) and “4.5 × 10^-3” all work.
- Choose the From prefix and the To prefix, or “(no prefix)” for the base unit. The swap button exchanges them.
- Type the Unit symbol, such as m, g, W or F, so the result reads naturally.
- Read the answer, its scientific notation and the factor between the two prefixes.
- Use Filter the table to find a prefix by name (nano), symbol (n) or power (10^-9 or 1e-9).
What it does and when to use it
Prefixes turn awkward numbers into readable ones: 0.000047 F becomes 47 µF, and 3300 kW becomes 3.3 MW. In science, engineering and electronics, you constantly move between them, and a slip of three places changes an answer by a factor of 1000. The table is a quick reference, and the converter does the shift exactly.
For a value in any form, the scientific notation converter writes it in scientific, engineering and E notation. Look up the values of constants in the physical constants table, and Greek symbols such as µ and Ω in the Greek alphabet reference.
How it works
Every prefix is a power of ten. Converting from a prefix with power a to one with power b multiplies the number by 10 to the power (a − b). The tool moves the decimal point as text, so there are no floating-point errors such as 0.30000000000000004. Everything runs in your browser.
The 24 SI prefixes
| Prefix | Symbol | Factor | Prefix | Symbol | Factor | |
|---|---|---|---|---|---|---|
| quetta | Q | 10³⁰ | deci | d | 10⁻¹ | |
| ronna | R | 10²⁷ | centi | c | 10⁻² | |
| yotta | Y | 10²⁴ | milli | m | 10⁻³ | |
| zetta | Z | 10²¹ | micro | µ | 10⁻⁶ | |
| exa | E | 10¹⁸ | nano | n | 10⁻⁹ | |
| peta | P | 10¹⁵ | pico | p | 10⁻¹² | |
| tera | T | 10¹² | femto | f | 10⁻¹⁵ | |
| giga | G | 10⁹ | atto | a | 10⁻¹⁸ | |
| mega | M | 10⁶ | zepto | z | 10⁻²¹ | |
| kilo | k | 10³ | yocto | y | 10⁻²⁴ | |
| hecto | h | 10² | ronto | r | 10⁻²⁷ | |
| deca | da | 10¹ | quecto | q | 10⁻³⁰ |
Worked examples
Power station output. 3.3 MW to kilowatts is 3300 kW; the factor is × 10³.
Capacitor value. 0.000047 F with no prefix to micro gives 47 µF, a factor of × 10⁶.
Wavelength of light. 450 nm to micrometres gives 0.45 µm, because nano to micro is a step of 10⁻³.
Limits and tips
- Symbols are case-sensitive: M is mega (10⁶) and m is milli (10⁻³). Filtering by “m” shows both.
- Only prefixes are converted. To change the unit itself, such as inches to centimetres, use a unit converter.
- Prefixes on squared units apply before squaring: 1 km² is 10⁶ m², not 10³ m². The converter does not handle powers of units.
Frequently asked questions
How many SI prefixes are there?
Why is the symbol for micro µ?
Can I combine two prefixes?
Are kilobytes 1000 or 1024 bytes?
Why does the result look so long?
Sources
- SI prefixes — Bureau International des Poids et Mesures (BIPM), accessed 2026-10-08
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