siprefix

SIprefix refers to the standardized set of prefixes used with SI units to denote multiples of ten. By attaching a prefix to a unit, a quantity can be expressed with more convenient numbers. The prefix and the unit form a single compound, written without a space (for example, 3 km, 0.25 μs).

The prefixes are defined and maintained for the International System of Units (SI) by the International Bureau of Weights and Measures (BIPM). They cover a range of powers of ten. Large-scale prefixes include kilo (k) 10^3, mega (M) 10^6, giga (G) 10^9, tera (T) 10^12, peta (P) 10^15, exa (E) 10^18, zetta (Z) 10^21, and yotta (Y) 10^24. Small-scale prefixes include deci (d) 10^-1, centi (c) 10^-2, milli (m) 10^-3, micro (μ) 10^-6, nano (n) 10^-9, pico (p) 10^-12, femto (f) 10^-15, atto (a) 10^-18, zepto (z) 10^-21, and yocto (y) 10^-24. In addition, deka (da) 10^1 and hecto (h) 10^2 are official prefixes used for larger multiples. Prefix symbols are case-sensitive (for example, k for kilo, M for mega, μ for micro); the micro symbol may be written as 'u' when the symbol is not available. Prefixes can be applied to any SI unit, yielding forms such as km, MHz, or μg.

These prefixes express decimal multipliers and are distinct from binary prefixes used in computing. They provide a concise, standardized way to convey magnitude in scientific and technical contexts.