Conversion formula

The conversion factor from decimeters to millimeters is 100, which means that 1 decimeter is equal to 100 millimeters:

1 dm = 100 mm

To convert 0.4 decimeters into millimeters we have to multiply 0.4 by the conversion factor in order to get the length amount from decimeters to millimeters. We can also form a simple proportion to calculate the result:

1 dm → 100 mm

0.4 dm → L_(mm)

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

L_(mm) = 0.4 dm × 100 mm

L_(mm) = 40 mm

The final result is:

0.4 dm → 40 mm

We conclude that 0.4 decimeters is equivalent to 40 millimeters:

0.4 decimeters = 40 millimeters

Alternative conversion

We can also convert by utilizing the inverse value of the conversion factor. In this case 1 millimeter is equal to 0.025 × 0.4 decimeters.

Another way is saying that 0.4 decimeters is equal to 1 ÷ 0.025 millimeters.

Approximate result

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

0.4 dm ≅ 40 mm

An alternative is also that one millimeter is approximately zero point zero two five times zero point four decimeters.

Conversion table

decimeters to millimeters chart

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