What is the difference between mega (M) and milli (m)?

Mega (M) means one million, 10⁶, while milli (m) means one thousandth, 10⁻³. Note the capital M is a million and lowercase m is a thousandth — case matters.

Are the newest SI prefixes included?

Yes — the 2022 additions ronna (R, 10²⁷), quetta (Q, 10³⁰), ronto (r, 10⁻²⁷) and quecto (q, 10⁻³⁰) are all in the table.

Kilo (symbol k) means one thousand, 10³. So 1 kilometre is 1000 metres and 1 kilogram is 1000 grams.

How many SI prefixes are there?

There are 24 SI prefixes in total, spanning 10³⁰ (quetta) down to 10⁻³⁰ (quecto), after the 2022 additions of ronna, quetta, ronto and quecto.

What is the symbol for micro?

Micro is the Greek letter µ (sometimes written "u" in plain text) and means one millionth, 10⁻⁶. For example, 1 µm is one micrometre, a millionth of a metre.

Is anything uploaded?

No — this is a static reference table that runs entirely in your browser.

Metric Prefixes Reference

This is a searchable reference of all SI (metric) prefixes, from quetta (10³⁰) down to quecto (10⁻³⁰), including the everyday ones (kilo, mega, giga, milli, micro, nano) and the 2022 BIPM additions. It is for students, engineers and anyone decoding a unit symbol.

How it works

Each SI prefix is a fixed power of ten that multiplies the base unit. To apply a prefix, multiply by its factor; to remove it, divide. The table lists the prefix name, its symbol, the power of ten, the full numeric factor, and the short-scale name (thousand, million, billion). Type in the search box to filter by name, symbol or scale.

Case matters: capital M is mega (a million) while lowercase m is milli (a thousandth) — mixing them up is a 10⁹ error.

Example

To convert 5 GW (gigawatts) to watts, apply giga = 10⁹:

5 × 1,000,000,000 = 5,000,000,000 W.

Prefix	Symbol	Factor
giga	G	10⁹ (billion)
mega	M	10⁶ (million)
kilo	k	10³ (thousand)
milli	m	10⁻³ (thousandth)
micro	µ	10⁻⁶ (millionth)
nano	n	10⁻⁹ (billionth)

Everything runs in your browser; nothing is uploaded.