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 40 decimeters into millimeters we have to multiply 40 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

40 dm → L_(mm)

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

L_(mm) = 40 dm × 100 mm

L_(mm) = 4000 mm

The final result is:

40 dm → 4000 mm

We conclude that 40 decimeters is equivalent to 4000 millimeters:

40 decimeters = 4000 millimeters

Alternative conversion

We can also convert by utilizing the inverse value of the conversion factor. In this case 1 millimeter is equal to 0.00025 × 40 decimeters.

Another way is saying that 40 decimeters is equal to 1 ÷ 0.00025 millimeters.

Approximate result

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

40 dm ≅ 4000 mm

An alternative is also that one millimeter is approximately zero times forty 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