1 kilometer in millimeters

Conversion

1 kilometer is equivalent to 1000000 millimeters.^[1]

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 1e-06 times 1 kilometer.

It can also be expressed as: 1 kilometer is equal to $\frac{1}{1e-06}$ millimeters.

Approximation

An approximate numerical result would be: one kilometer is about one million millimeters, or alternatively, a millimeter is about zero times one kilometer.

Units involved

This is how the units in this conversion are defined:

Kilometers

The kilometre or kilometer (American spelling) is a unit of length in the metric system, equal to one thousand metres (kilo being the SI prefix for 1000). It is now the measurement unit used officially for expressing distances between geographical places on land in most of the world; notable exceptions are the United States and the road network of the United Kingdom where the statute mile is the official unit used.

Wikipedia page of kilometers

Millimeters

The millimetre or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length.

Wikipedia page of millimeters

Footnotes

[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).

Results may contain small errors due to the use of floating point arithmetic.