About the km to mm calculation
One kilometer is exactly 1,000,000 millimeters, so converting between them is a single multiplication. Enter any value above and the result updates as you type. The standard road-distance unit in most of the world. The standard fine unit on engineering drawings and rainfall figures.
Formula
mm = km × 1,000,000
1 km = 1,000,000 mm
1 mm = 0.000001 kmWorked example
To convert 10 km, multiply by 1,000,000: 10 × 1,000,000 = 10,000,000 mm.
Frequently asked questions
How many millimeters are in a kilometer?
There are 1,000,000 millimeters in one kilometer. To convert any amount, multiply the number of kilometers by 1,000,000.
How do I convert millimeters back to kilometers?
Divide instead of multiplying, or equivalently multiply by 0.000001. One millimeter is 0.000001 kilometers.
Is this conversion exact?
Yes. Since the international agreement of 1959, the relationship between kilometers and millimeters is defined exactly rather than measured, so the only rounding here is in how many decimal places we show.
Where is each of these units used?
Kilometers: the standard road-distance unit in most of the world. Millimeters: the standard fine unit on engineering drawings and rainfall figures.
Sources
- NIST Special Publication 811 — Guide for the Use of the International System of Units