420 kilometers in millimeters

Conversion formula
How to convert 420 kilometers to millimeters?

We know (by definition) that: $1\mathrm{km}=1000000\mathrm{mm}$

We can set up a proportion to solve for the number of millimeters.

Now, we cross multiply to solve for our unknown $x$:

Conclusion: 420 ⁢ km = 420000000 ⁢ mm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 2.38095238095238e-09 times 420 kilometers.

It can also be expressed as: 420 kilometers is equal to $\frac{1}{\mathrm{2.38095238095238e-09}}$ millimeters.

Approximation

An approximate numerical result would be: four hundred and twenty kilometers is about four hundred and twenty million millimeters, or alternatively, a millimeter is about zero times four hundred and twenty kilometers.