How si prefix reference works
SI prefixes attach to any unit to scale it by a power of ten: kilometre, megabyte, gigawatt, nanosecond. The system currently has 24 prefixes spanning 10³⁰ (quetta) down to 10⁻³⁰ (quecto), and they follow a strict grammar — symbols are case-sensitive (m is milli, M is mega), most are one letter, and deca is the only two-letter symbol (da). This table lists every prefix with its symbol, its power of ten, and where the name comes from; a search field resolves names, symbols or exponents like 1e9.
The ladder is built in steps of a thousand: kilo, mega, giga, tera, peta, exa, zetta, yotta — each is 1000 times the last, mirrored downwards by milli, micro, nano, pico and friends. Between the thousand-steps sit hecto, deca, deci and centi, which engineering rarely uses but daily life does (hectopascals in weather reports, centimetres on rulers). In 2022 the BIPM added ronna (R, 10²⁷), quetta (Q, 10³⁰), ronto (r, 10⁻²⁷) and quecto (q, 10⁻³⁰) because data science was outgrowing yotta — a ronnabyte is a trillion terabytes.
The converter multiplies by the exponent gap: 5.2 km to base units is 5.2 × 10³ = 5200, and 250 ms to seconds is 0.25, because milli sits three steps (10⁻³) below the unit. Converting between any two prefixes is the same subtraction — the tool computes value × 10^(from − to). One classic trap is built into the system itself: the kilogram is the only SI unit whose name contains a prefix, so mass prefixes attach to the gram (mg, kg never becomes "kilo-kilogram"), and the megagram survives only as its synonym, the tonne.