Millimeters to Kilometers Converter

About the mm to km calculation

One millimeter is exactly 0.000001 kilometers, so converting between them is a single multiplication. Enter any value above and the result updates as you type. The standard fine unit on engineering drawings and rainfall figures. The standard road-distance unit in most of the world.

Formula

km = mm × 0.000001

1 mm = 0.000001 km
1 km = 1,000,000 mm

Worked example

To convert 100 mm, multiply by 0.000001: 100 × 0.000001 = 0.0001 km.

Frequently asked questions

How many kilometers are in a millimeter?

There are 0.000001 kilometers in one millimeter. To convert any amount, multiply the number of millimeters by 0.000001.

How do I convert kilometers back to millimeters?

Divide instead of multiplying, or equivalently multiply by 1,000,000. One kilometer is 1,000,000 millimeters.

Is this conversion exact?

Yes. Since the international agreement of 1959, the relationship between millimeters and kilometers 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?

Millimeters: the standard fine unit on engineering drawings and rainfall figures. Kilometers: the standard road-distance unit in most of the world.

Sources

• NIST Special Publication 811 — Guide for the Use of the International System of Units