640 kilometers in millimeters

Conversion formula
How to convert 640 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: 640 ⁢ km = 640000000 ⁢ mm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 1.5625e-09 times 640 kilometers.

It can also be expressed as: 640 kilometers is equal to $\frac{1}{\mathrm{1.5625e-09}}$ millimeters.

Approximation

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