21 decimeters in millimeters

Conversion formula
How to convert 21 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: 21 ⁢ dm = 2100 ⁢ mm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 0.000476190476190476 times 21 decimeters.

It can also be expressed as: 21 decimeters is equal to $\frac{1}{\mathrm{0.000476190476190476}}$ millimeters.

Approximation

An approximate numerical result would be: twenty-one decimeters is about two thousand, one hundred millimeters, or alternatively, a millimeter is about zero times twenty-one decimeters.