SIPrefixe

SIPrefixe, or SI prefixes, are decimal multipliers used with the units of the International System of Units (SI) to express multiples and submultiples of a unit. They provide a concise way to denote large or small quantities and are applied to SI base and derived units.

They are standardized by the organizations that administer the SI, notably the International Bureau of Weights and Measures (BIPM) under the General Conference on Weights and Measures (CGPM). The system was formalized in 1960 as part of the modern SI, and prefixes represent powers of ten to facilitate clear communication of magnitude.

Common 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). For small scales, 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 2022, additional prefixes ronna (R) for 10^27 and quetta (Q) for 10^30 were adopted to extend the range beyond yotta.

Prefix symbols are case sensitive: for example, k denotes kilo, M denotes mega, while m denotes milli and μ denotes micro. Prefixes are attached to SI units (for instance kilometer, megawatt, microsecond) and are not generally used with non-SI units. In practice, prefixes improve readability and precision, and a single prefix is typically used per unit.