Convert millimetres to kilometres
1 mm = 0.000001 km
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How many kilometres are in a millimetre?
One millimetre is 0.000001 kilometres. To convert any amount, multiply by 0.000001. Going the other way, one kilometre is 1000000 millimetres.
What is the formula to convert mm to km?
Multiply the millimetre figure by 0.000001. So km = mm × 0.000001. For a quick mental estimate, dividing by about 1000000 gets you close enough for most everyday purposes.
What does a millimetre actually look like?
One millimetre is roughly the thickness of a credit card, which is 0.76 mm. The millimetre is the working unit of engineering drawings and machining tolerances almost everywhere metric is used, because it avoids decimals for most part dimensions.
And what is a kilometre?
One kilometre is about a 12-minute walk. The kilometre is the standard road-distance unit everywhere except the United States, the United Kingdom and a handful of small territories.
Is this conversion exact?
Yes. Since the 1959 international yard and pound agreement, the imperial and metric systems are related by exact definitions rather than measurements — the inch is exactly 25.4 mm and the pound exactly 0.45359237 kg. Everything derived from those, including this conversion, is therefore exact. Round at the end rather than partway through, since rounding mm before converting introduces an error the conversion then multiplies.
About mm to km
How to convert millimetres to kilometres
Multiply by 0.000001. One millimetre is 0.000001 kilometres, and one kilometre is 1000000 millimetres.
km = mm × 0.000001
Worked example
10 mm = 0.00001 km. For a sense of scale, one millimetre is roughly the thickness of a credit card, which is 0.76 mm, and one kilometre is about a 12-minute walk.
About the millimetre
The millimetre is the working unit of engineering drawings and machining tolerances almost everywhere metric is used, because it avoids decimals for most part dimensions.
About the kilometre
The kilometre is the standard road-distance unit everywhere except the United States, the United Kingdom and a handful of small territories.
Quick reference
| millimetres | kilometres |
|---|---|
| 1 mm | 0.000001 km |
| 2 mm | 0.000002 km |
| 5 mm | 0.000005 km |
| 10 mm | 0.00001 km |
| 25 mm | 0.000025 km |
| 50 mm | 0.00005 km |
| 100 mm | 0.0001 km |
| 1000 mm | 0.001 km |
Getting it right
This conversion is exact by definition, so the only limit on accuracy is how many digits you keep. Round at the end rather than partway through — rounding mm to a whole number before converting introduces an error that the conversion then multiplies.
Other length conversions
Convert kilometres back to millimetres, or pick any other pair with the full unit converter. Related: mm to m, mm to cm, mm to mi.