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Convert mm to km
1 mm = 0.000001 km
Type a value in millimetres and the answer in kilometres appears as you go. The conversion is exactly 0.000001 km to the millimetre, and it happens on your own machine — this page asks nothing of a server once it has loaded.
Where it runs
In your browser. The number you type is never part of a request.
Exact by definition
1 mm is exactly 0.000001 km — a definition, not a rounded factor.
Answers as you type
No button, no wait. The worked answer is already on the page before any script runs.
Millimetre and Kilometre
Millimetres are what engineering drawings and datasheets use, because a whole number of them is precise enough for almost anything made by machine and avoids a decimal point that can be lost in a photocopy.
Kilometres are the road distance nearly everywhere outside the United States and the United Kingdom, which is why converting them is usually about reading a map or a race entry.
millimetres to kilometres in practice
210 mm is 0.00021 km
— the short side of a sheet of A4 paper.
1800 mm is 0.0018 km
— a standard interior doorway.
millimetres to kilometres at a glance
| mm | km |
|---|---|
| 1 | 0.000001 |
| 2 | 0.000002 |
| 3 | 0.000003 |
| 5 | 0.000005 |
| 10 | 0.00001 |
| 20 | 0.00002 |
| 50 | 0.00005 |
| 100 | 0.0001 |
Every figure here is computed from the same definition the calculator uses, so the table cannot drift away from the answer above it.
Convert mm to km: common questions
How many kilometres are in a millimetre?
Exactly 0.000001. One millimetre is 0.000001 kilometres, and the box above will do it for any figure you type.
Is this conversion exact, or rounded?
The ratio is exact. It is not a rounded constant typed into a table: it is derived from the definitions of the two units, so it agrees with any other correct converter to as many digits as you care to compare.
Why does another converter show a slightly different number?
Almost always rounding rather than disagreement. Many converters cut the answer to two or four decimals, and some carry a factor that was rounded before the multiplication rather than after. The figures here are computed from the exact definitions and only rounded on the way to the screen.
Where these figures come from
The claims this page makes about length units are checkable, and these are the documents that settle them.
How this page works
The factor is a constant in the page and the arithmetic is four operations, so nothing is sent anywhere and nothing needs to be. The number you type never leaves the browser — there is no request for it to travel in.