21 millimeters in centimeters

Conversion formula
How to convert 21 millimeters to centimeters?

We know (by definition) that: $1\mathrm{mm}=0.1\mathrm{cm}$

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

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

Conclusion: 21 ⁢ mm = 2.1 ⁢ cm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 centimeter is equal to 0.476190476190476 times 21 millimeters.

It can also be expressed as: 21 millimeters is equal to $\frac{1}{\mathrm{0.476190476190476}}$ centimeters.

Approximation

An approximate numerical result would be: twenty-one millimeters is about zero centimeters, or alternatively, a centimeter is about zero point four eight times twenty-one millimeters.