SI Prefixes
SI prefixes are standardized multipliers attached to a base unit to express very large or very small quantities.
They apply to any SI unit: meters, grams, seconds, volts, watts, hertz, and so on.
Common Prefixes
The table is ordered from the largest prefix down to the smallest. The base unit (factor 1) sits in the middle.
| Prefix | Symbol | Factor | Power | Example |
|---|---|---|---|---|
| tera | T | 1,000,000,000,000 | 10¹² | TB, THz |
| giga | G | 1,000,000,000 | 10⁹ | GHz, GW |
| mega | M | 1,000,000 | 10⁶ | MW, MΩ |
| kilo | k | 1,000 | 10³ | km, kg, kV, kWh |
| — | — | 1 | 10⁰ | m, g, V, W |
| deci | d | 0.1 | 10⁻¹ | dl, dm |
| centi | c | 0.01 | 10⁻² | cm |
| milli | m | 0.001 | 10⁻³ | mm, mV, ms |
| micro | µ | 0.000001 | 10⁻⁶ | µs, µm, µF |
| nano | n | 0.000000001 | 10⁻⁹ | nm, ns |
| pico | p | 0.000000000001 | 10⁻¹² | pF, ps |
info
The "main" sequence (kilo => mega => giga => tera and milli => micro => nano => pico) goes in steps of 1,000 (10³) per prefix. Deci and centi sit between the base unit and milli as smaller intermediate steps (10⁻¹ and 10⁻²).
Scaling Between Prefixes
Each prefix is just a power of 10 (see the Power column above). To convert between two prefixes, take the difference of their powers and apply it as steps.
Upward (Smaller => Larger)
Formula: value / 10^steps
Example: 2,500 mV => V
Steps: mV (10⁻³) => V (10⁰) = 3 powers of 10
2,500 mV / 10³ = 2.5 V
Downward (Larger => Smaller)
Formula: value x 10^steps
Example: 5 km => mm
Steps: km (10³) => mm (10⁻³) = 6 powers of 10
5 km x 10⁶ = 5,000,000 mm
Common Examples in Practice
- kV — kilovolt, 1,000 V (high-voltage power lines)
- mA — milliampere, 0.001 A (small electronics)
- MHz — megahertz, 1,000,000 Hz (radio frequencies, CPU clocks)
- nm — nanometer, 0.000000001 m (semiconductor process nodes, light wavelengths)
- kWh — kilowatt-hour, 1,000 Wh (electricity bills)
- µF — microfarad, 0.000001 F (capacitor values)
See Also
- Bit, Byte & Unit Conversions: applies these prefixes to bytes (decimal) and contrasts them with the binary IEC prefixes (kibi, mebi, gibi, etc.)
- Electrical Units: uses these prefixes for V, A, W, Wh, etc.