Conversion formula

The conversion factor from millimeters to kilometers is 1.0E-6, which means that 1 millimeter is equal to 1.0E-6 kilometers:

1 mm = 1.0E-6 km

To convert 21 millimeters into kilometers we have to multiply 21 by the conversion factor in order to get the length amount from millimeters to kilometers. We can also form a simple proportion to calculate the result:

1 mm → 1.0E-6 km

21 mm → L_(km)

Solve the above proportion to obtain the length L in kilometers:

L_(km) = 21 mm × 1.0E-6 km

L_(km) = 2.1E-5 km

The final result is:

21 mm → 2.1E-5 km

We conclude that 21 millimeters is equivalent to 2.1E-5 kilometers:

21 millimeters = 2.1E-5 kilometers

Alternative conversion

We can also convert by utilizing the inverse value of the conversion factor. In this case 1 kilometer is equal to 47619.047619048 × 21 millimeters.

Another way is saying that 21 millimeters is equal to 1 ÷ 47619.047619048 kilometers.

Approximate result

For practical purposes we can round our final result to an approximate numerical value. We can say that twenty-one millimeters is approximately zero kilometers:

21 mm ≅ 0 km

An alternative is also that one kilometer is approximately forty-seven thousand six hundred nineteen point zero four eight times twenty-one millimeters.

Conversion table

millimeters to kilometers chart

For quick reference purposes, below is the conversion table you can use to convert from millimeters to kilometers