21 millimeters in decimeters

Result

The conversion result is: 21 millimeters is equivalent to 0.21 decimeters.^[1]

Conversion formula
How to convert 21 millimeters to decimeters?

We know (by definition) that: 1 mm = 0.01 dm.

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

1 mm / 21 mm = 0.01 dm / x dm

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

x dm = (21 mm / 1 mm) * 0.01 dm → x dm = 0.21 dm

Conclusion:

21 mm = 0.21 dm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 decimeter is equal to 4.76190476190476 times 21 millimeters.

It can also be expressed as: 21 millimeters is equal to 1 / 4.76190476190476 decimeters.

Approximation

An approximate numerical result would be: twenty-one millimeters is about zero decimeters, or alternatively, a decimeter is about four point seven five times twenty-one millimeters.