Metric Prefix Converter
Same value in every unit
| Unit | Value |
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The capital letter is not decoration
M is mega. m is milli. They differ by a factor of a billion, and a datasheet that says mA when it means MA is not a typo you can shrug at. The rule is simple: everything from mega upwards is capitalised, everything below is lower case, and kilo is the one exception — a lower-case k, never K.
Kilobytes are where this gets messy
In SI, kilo means exactly 1000. Computing borrowed the word for 1024, which is close enough to be confusing and different enough to matter: over a terabyte the gap is about 10%. That is the whole explanation for why a 1 TB drive shows as roughly 931 GB — the manufacturer counted in 1000s, the operating system divided by 1024s. Neither is lying. The unambiguous forms are KiB, MiB and GiB.
One prefix at a time
A millimicrometre is not a unit; it is a nanometre. Prefixes never stack. The kilogram is the awkward exception in the other direction — it is the SI base unit even though it already has a prefix, so a thousandth of it is a gram and a millionth is a milligram, not a microkilogram.
The newest ones
Ronna, quetta, ronto and quecto joined the SI in 2022, taking the range out to 10³⁰ and down to 10⁻³⁰. They were added mainly because global data volumes were running out of room above yotta.
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Frequently Asked Questions
Everything from mega upwards takes a capital — M, G, T, P, E, Z, Y, R, Q — and kilo is a lower-case k. Below that they are all lower case. It matters: M is mega and m is milli, a difference of a billion, and K is not a valid SI prefix at all.
In SI, kilo is exactly 1000, and that is what this converter uses. Computing has long used 1024 for the same word, which is why a "1 TB" drive shows as about 931 GB in an operating system that divides by 1024. The unambiguous binary prefixes are kibi, mebi and gibi — KiB, MiB, GiB.
The newest prefixes, added to the SI in 2022 along with ronto and quecto at the small end. They extend the range to 10³⁰ and 10⁻³⁰, mostly for data and for astronomy.
Because m was already taken by milli. The correct character is µ (U+00B5 or the Greek µ), and "u" is a common substitute where a keyboard cannot produce it.
No. A millimicrometre is not valid — it is a nanometre. Only one prefix is allowed at a time, and the kilogram is the odd exception: it is the SI base unit despite already carrying a prefix, so a millionth of a kilogram is a milligram, not a microkilogram.