40 decimeters in millimeters

Conversion formula
How to convert 40 decimeters to millimeters?

We know (by definition) that: $1\mathrm{dm}=100\mathrm{mm}$

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

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

Conclusion: 40 ⁢ dm = 4000 ⁢ mm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 0.00025 times 40 decimeters.

It can also be expressed as: 40 decimeters is equal to $\frac{1}{\mathrm{0.00025}}$ millimeters.

Approximation

An approximate numerical result would be: forty decimeters is about four thousand millimeters, or alternatively, a millimeter is about zero times forty decimeters.