Millimeters to Decimeters
An instant millimeters-to-decimeters converter, with the formula and a reference table below.
| Millimeters | Decimeters |
|---|---|
| 1 mm | 0.01 dm |
| 2 mm | 0.02 dm |
| 3 mm | 0.03 dm |
| 5 mm | 0.05 dm |
| 10 mm | 0.1 dm |
| 25 mm | 0.25 dm |
| 50 mm | 0.5 dm |
| 100 mm | 1 dm |
How to use
- Enter a value in the Millimeters field.
- The Decimeters figure appears immediately — no button to press.
- Typing in the Decimeters field converts back to Millimeters the same way.
- Use the reference table for the values that come up most often.
Millimeters to Decimeters formula
Converting millimeters to decimeters is a single multiplication by 0.01.
dm = mm × 0.01
Put another way, one millimeter is exactly 1/100 of a decimeter.
Why this factor: the millimeter and the decimeter are both defined against the meter, so dividing one definition by the other gives 0.01 directly. Both definitions are set out in full below.
To go the other way, divide by 0.01 — or use the Decimeters to Millimeters converter, which is the same calculation reversed.
Worked example
Given 100 mm, multiplying by 0.01 yields 1 dm.
100 mm × 0.01 = 1 dm
The converter above does this for any value you type, in either direction.
What is a millimeter?
A millimeter is one thousandth of a meter — the working precision unit of manufacturing and construction.
Definition: Exactly 0.001 meter by SI prefix definition.
Where it is used: Engineering drawings, machining tolerances, timber and steel dimensions, rainfall totals.
What is a decimeter?
A decimeter is one tenth of a meter — 10 centimeters.
Definition: Exactly 0.1 meter by SI prefix definition.
Where it is used: Rare in everyday speech, but it matters because a cubic decimeter is exactly one liter.
Worth knowing: The decimeter's real importance is volumetric: 1 dm³ = 1 L exactly, which is where the liter comes from.
Millimeters vs Decimeters
The millimeter and the decimeter belong to the same family of units, so converting between them is usually a matter of shifting a decimal point or applying a small whole-number factor.
Frequently asked questions
How many decimeters are in a millimeter?
One millimeter equals 0.01 decimeters.
What is the formula to convert millimeters to decimeters?
Multiply the number of millimeters by 0.01. To reverse it, divide by 0.01 instead.
How do I convert decimeters back to millimeters?
Divide by 0.01, which is the same as multiplying by 100.
How many decimeters are in 10 millimeters?
10 mm works out to 0.1 dm.
Is there anything to watch out for with decimeters?
The decimeter's real importance is volumetric: 1 dm³ = 1 L exactly, which is where the liter comes from.
How is the millimeter defined?
Exactly 0.001 meter by SI prefix definition.