640 millimeters in decimeters

Conversion formula
How to convert 640 millimeters to decimeters?

We know (by definition) that: $1\mathrm{mm}=0.01\mathrm{dm}$

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

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

Conclusion: 640 ⁢ mm = 6.4 ⁢ dm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 decimeter is equal to 0.15625 times 640 millimeters.

It can also be expressed as: 640 millimeters is equal to $\frac{1}{\mathrm{0.15625}}$ decimeters.

Approximation

An approximate numerical result would be: six hundred and forty millimeters is about zero decimeters, or alternatively, a decimeter is about zero point one six times six hundred and forty millimeters.