SIprefixed

SIprefixed refers to the system of prefixes attached to SI units to express multiples and submultiples of those units in powers of ten. Each prefix represents a fixed factor, and combining it with a unit multiplies the unit’s value by that factor. The prefixes are standardized and maintained as part of the International System of Units (SI) by the International Bureau of Weights and Measures (BIPM). They enable concise expression of very large or very small quantities in science, engineering, and everyday measurements.

The current set spans from 10^24 to 10^-24. 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). Medium-scale prefixes such as deca (da, 10^1) and hecto (h, 10^2) are official but rarely used. 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). Each prefix has a specific symbol, with case sensitivity important (for example M vs m; μ for micro; in plain text often written as u). The prefixes are decimal-based, not binary, and are intended to be used with SI units only.

Usage guidelines emphasize attaching the prefix symbol directly to the unit (no space). A space separates the numeric value from the unit, as in 3 km, 2.5 μs, or 6 MW. The system is widely used across disciplines, though not all prefixes are common with every unit, and some contexts prefer avoiding certain combinations for clarity.