Millimeters to Decimeters
Convert millimeters to decimeters instantly. 1 mm = 0.01 dm. Includes the exact factor, a conversion table of common values and the definition of both units.
How to convert millimeters to decimeters
To convert millimeters to decimeters, divide by 100 (multiply by 0.01). The relationship is fixed, so the same factor works for any quantity — there is nothing to look up and nothing that changes with temperature, location or context.
dm = mm × 0.01
Millimeters to Decimeters conversion table
The values people look up most often, rounded for reading. Use the calculator above for anything in between.
| 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 |
| 20 mm | 0.2 dm |
| 25 mm | 0.25 dm |
| 50 mm | 0.5 dm |
| 100 mm | 1 dm |
| 500 mm | 5 dm |
| 1,000 mm | 10 dm |
What is a millimeter?
A thousandth of a metre. The default fine unit on metric engineering drawings.
What is a decimeter?
A tenth of a metre. Rare in practice, but it is the cube root of the litre.
The formula
dm = mm × 0.01
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Millimeters to Decimeters
- Type the number of millimeters you want to convert.
- Read the result in decimeters straight away — there is no button to press.
- Check the table below for the values that come up most often, or reverse the conversion with the linked decimeters to millimeters page.
Millimeters to Decimeters — frequently asked questions
How many decimeters are in a millimeter?
One millimeter equals 0.01 dm. dm = mm × 0.01
What is the formula to convert millimeters to decimeters?
The formula is dm = mm × 0.01. It is an exact definition rather than an approximation, so the conversion never drifts no matter how large the number.
How do I convert decimeters back to millimeters?
Divide instead of multiplying: one decimeter is 100 mm. The reverse converter is linked in the related tools list.
Is this conversion exact?
Yes. Both units are defined against the same base unit by international agreement, so the factor is exact — any rounding you see is only in the display, which you can widen by entering more decimal places.
Is this millimeters to decimeters free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
What people search for
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 15, 2026 · Calculation runs client-side · No data collected · Report an error