Conversion formula

The conversion factor from millimeters to decimeters is 0.01, which means that 1 millimeter is equal to 0.01 decimeters:

1 mm = 0.01 dm

To convert 21 millimeters into decimeters we have to multiply 21 by the conversion factor in order to get the length amount from millimeters to decimeters. We can also form a simple proportion to calculate the result:

1 mm → 0.01 dm

21 mm → L_(dm)

Solve the above proportion to obtain the length L in decimeters:

L_(dm) = 21 mm × 0.01 dm

L_(dm) = 0.21 dm

The final result is:

21 mm → 0.21 dm

We conclude that 21 millimeters is equivalent to 0.21 decimeters:

21 millimeters = 0.21 decimeters

Alternative conversion

We can also convert by utilizing the inverse value of the conversion factor. In this case 1 decimeter is equal to 4.7619047619048 × 21 millimeters.

Another way is saying that 21 millimeters is equal to 1 ÷ 4.7619047619048 decimeters.

Approximate result

For practical purposes we can round our final result to an approximate numerical value. We can say that twenty-one millimeters is approximately zero point two one decimeters:

21 mm ≅ 0.21 dm

An alternative is also that one decimeter is approximately four point seven six two times twenty-one millimeters.

Conversion table

millimeters to decimeters chart

For quick reference purposes, below is the conversion table you can use to convert from millimeters to decimeters