Metric Prefix Converter
SI metric prefixes let you write very large or very small numbers without long strings of zeros. This converter takes a value expressed in one prefix and re-expresses it in any other, from quecto (10 to the power -30) up to quetta (10 to the power 30). Because every prefix is an exact power of ten defined by NIST and the BIPM, the conversion is exact: choose your source prefix, your target prefix, enter a number, and read the result. This is useful for science, engineering, data sizes, frequencies, and unit work where moving between micro, milli, kilo, mega and beyond is routine.
Metric prefix conversion formula
Each prefix maps to an exponent e (power of ten)
Conversion factor = 10 ^ (e_from - e_to)
Converted value = value * conversion factor
Example: 5 kilo to milli = 5 * 10 ^ (3 - (-3)) = 5,000,000
Prefixes are exact powers of ten, so the conversion factor carries no rounding error. The displayed result may round at 2 decimal places, and very small magnitudes are shown in scientific notation.
SI prefix context
- NIST and the BIPM define 24 SI prefixes spanning 60 orders of magnitude.
- Prefixes for one million and above use uppercase symbols (M, G, T, P, E, Z, Y, R, Q).
- Prefixes below one million use lowercase symbols (k, h, da, d, c, m and Greek mu for micro).
- Ronna, quetta, ronto and quecto were adopted by the CGPM in 2022.
- SI prefixes are decimal (powers of ten); binary data prefixes such as kibi (2 to the power 10) are a separate IEC standard.
Metric prefix converter: frequently asked questions
What is a metric (SI) prefix?
An SI prefix is a multiplier attached to a base unit to express very large or very small quantities, such as kilo (1,000 times) or milli (one thousandth). NIST and the BIPM define 24 prefixes, each a fixed power of ten, ranging from quecto (10 to the power -30) up to quetta (10 to the power 30).
How does this converter work?
Each prefix maps to an exponent of ten. To convert a value from one prefix to another, multiply the value by 10 raised to the difference of the two exponents. For example, converting 5 kilo (exponent 3) to milli (exponent -3) multiplies by 10 to the power 6, giving 5,000,000 milli.
What are the newest SI prefixes?
In 2022 the General Conference on Weights and Measures added ronna (10 to the power 27), quetta (10 to the power 30), ronto (10 to the power -27), and quecto (10 to the power -30). These extend the system to describe quantities such as the mass of Earth in ronnagrams.
Why does kilo use a lowercase k but mega uses a capital M?
By SI convention prefixes for one million and above use uppercase symbols (M, G, T), while prefixes below one million use lowercase symbols (k, m, u). This avoids confusion: capital K is the symbol for kelvin, so kilo must be lowercase k.
Is the result exact?
Yes. SI prefixes are exact powers of ten by definition, so the conversion factor is exact. Any rounding you see is only in the display of the final number, not in the underlying calculation.
Official sources
- NIST Physics Laboratory: SI prefixes.
- NIST Office of Weights and Measures: Metric (SI) prefixes.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.