SI Prefixes Reference
Search the full modern SI prefix range from 10^-30 through 10^30.
Look up official SI decimal prefixes
SI prefixes attach named decimal scales to units, allowing extremely large or small quantities to be written compactly. This reference includes all currently defined positive and negative prefixes from quecto and ronto through ronna and quetta, along with the long-established intermediate names. Search by full name, exact symbol, or exponent to narrow the table while retaining the power of ten and exponential multiplier.
The default search kilo returns symbol k, exponent 3, and multiplier 1,000. Searching quecto returns symbol q, exponent negative 30, and multiplier 1e-30. The table also shows why symbol case matters: lowercase m is milli at 10 to the negative 3, while uppercase M is mega at 10 to the positive 6. Deca uses the two-letter symbol da.
Use symbol case and powers carefully
The reference data is embedded and searched entirely in your browser, with no remote lookup. Prefixes scale units but do not change the physical quantity, measurement accuracy, or unit definition. Preserve symbol capitalization, avoid mixing decimal SI prefixes with binary storage prefixes, and write a space between the numeric value and unit symbol according to the conventions required by the document or technical field.
Frequently Asked Questions
What range does the table cover?
It covers official prefixes from quecto at 10 to the negative 30 through quetta at 10 to the positive 30.
Are prefix symbols case-sensitive?
Yes. For example, lowercase m means milli while uppercase M means mega.
Why are there no prefixes for every exponent?
SI assigns prefixes only to selected powers of ten, primarily steps of three beyond the small decimal prefixes.
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