How many milligrams in a kilogram?

One million. Kilo is 10³ and milli is 10⁻³, so the shift is six orders of magnitude.

Is a kilobyte 1000 or 1024 bytes?

In SI terms, 1,000. Computing has historically used 1,024 and labelled it "KB" anyway, which is why the separate binary prefixes — kibibyte, mebibyte, gibibyte — were introduced in 1998.

Metric Prefix Converter

Convert a value between metric prefixes, from pico through tera, for any SI unit.

Draft — figures checked, awaiting an editorial read. Not indexed.

Result—

Formula: Result = amount × (10^source exponent ÷ 10^target exponent). Prefixes are pure powers of ten.

What this calculates

This shifts a value between metric prefixes for whatever unit you are working in — watts, grams, metres, hertz, litres. The prefix is independent of the unit, which is the point of the SI system and its main advantage over customary units: once you know that kilo means a thousand, you know it in every context, whereas customary units have to memorise separately that twelve inches make a foot and three feet make a yard.

How it works

Every prefix is a power of ten, and converting is a matter of dividing one power by the other. Going from kilo (10³) to milli (10⁻³) is a shift of six orders of magnitude, so the number multiplies by a million. The prefixes here run from pico at 10⁻¹² to tera at 10¹², which spans essentially everything encountered outside particle physics and astronomy. Deca and hecto are included for completeness though they are rarely used in practice — hectares and hectopascals being the notable survivors.

Worked example

Converting 1 kilowatt to milliwatts: kilo is 10³ and milli is 10⁻³, so the shift is 10⁶ and the answer is 1,000,000 mW. A more everyday one: a 2.4 gigahertz signal in megahertz is 2.4 × 10⁹ ÷ 10⁶ = 2,400 MHz — the same frequency written two ways, which is why WiFi is described using both numbers interchangeably.

Common mistakes

Capitalisation, which genuinely changes meaning: M is mega and m is milli, a factor of a billion apart. Similarly k is kilo while K is kelvin. Second, assuming the data-storage prefixes work the same way — in computing, kilo often means 1,024 rather than 1,000, which is a different system entirely and the reason the kibi/mebi/gibi prefixes exist. Third, forgetting that prefixes on squared or cubed units cube too: a cubic centimetre is 10⁻⁶ cubic metres, not 10⁻². It is also worth knowing that the range shown here is not the whole system. The General Conference on Weights and Measures added four more prefixes in November 2022 — ronna and quetta at 10²⁷ and 10³⁰, ronto and quecto at 10⁻²⁷ and 10⁻³⁰ — largely because global data volumes were approaching the top of the existing scale. They are omitted here because nothing outside astronomy and data forecasting uses them yet.

Common questions

How many milligrams in a kilogram?: One million. Kilo is 10³ and milli is 10⁻³, so the shift is six orders of magnitude.
Is a kilobyte 1000 or 1024 bytes?: In SI terms, 1,000. Computing has historically used 1,024 and labelled it "KB" anyway, which is why the separate binary prefixes — kibibyte, mebibyte, gibibyte — were introduced in 1998.