Millimeter is 0.001 meter units.
Millimeters to Decimeters Converter — mm to dm
Convert Millimeter (mm) to Decimeter (dm) using the exact conversion factor (1 millimeter = 0.01 decimeter). See the formula, worked examples, conversion table, history, and common uses.
Millimeters to Decimeters converter
Converter
Length Converter
Convert SI, imperial, US customary, astronomical, scientific, and historical length units.
Context values
Some unit families need one extra value for a physically accurate result.
Decimeter is 0.1 meter units.
Result = input x 0.001 / 0.1.
Length uses the meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Millimeters to Decimeters
Millimeter and Decimeter both measure length. Millimeter is most often used for engineering drawings and manufacturing tolerances worldwide (including in the us).
Formula
decimeters = millimeters × 0.01
This factor comes from each unit's defined relationship to the category's base unit: 1 millimeter equals 0.001 base units, and 1 decimeter equals 0.1 base units, so dividing one by the other gives the direct millimeter-to-decimeter factor of 0.01.
Simple example
1 mm × 0.01 = 0.01 dm
1 millimeter = 0.01 decimeters.
Real-world example
10 mm × 0.01 = 0.1 dm
10 millimeters = 0.1 decimeters.
Conversion table
| Millimeter (mm) | Decimeter (dm) |
|---|---|
| 1 mm | 0.01 dm |
| 5 mm | 0.05 dm |
| 10 mm | 0.1 dm |
| 21.0975 mm | 0.210975 dm |
| 42.195 mm | 0.42195 dm |
| 100 mm | 1 dm |
Reverse conversion: Decimeter to Millimeter
0.01 dm × 100 = 1 mm
0.01 decimeters = 1 millimeter.
millimeters = decimeters × 100
For a page dedicated to this direction, see Decimeter to Millimeter.
Understanding the Millimeter
Millimeter (mm) measures distance. A millimeter is one-thousandth of a meter. It is classified as a SI derived (metric prefix) unit.
Where it's used: Standard small/precision length unit worldwide, including in US engineering and manufacturing
Uses of the Millimeter today
- Engineering drawings and manufacturing tolerances worldwide (including in the US)
- Rainfall measurement in most countries
- Small-scale everyday measurement (screen sizes, hardware)
History of the Millimeter
The millimeter follows from the meter via the 'milli-' SI prefix (10⁻³). It is notable as one of the few metric units in routine US technical/engineering use, since precision manufacturing and electronics are often specified in millimeters even in the US.
Historical origin. Millimeter was not the invention of a single named person; it developed through the process described above.
Understanding the Decimeter (dm)
Decimeter is 0.1 meter units.
Millimeter — sources
- BIPM SI Brochure — SI prefixes — Defines 'milli-' as the prefix for 10⁻³.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many decimeters are in 1 millimeter?
1 millimeter equals 0.01 decimeters, using the exact defined conversion factor rather than an estimate.
How do I convert millimeter to decimeter?
Multiply the millimeter value by 0.01. The converter above does this instantly to whatever precision you set.
How do I convert decimeter back to millimeter?
Use the reverse factor: 1 decimeter equals 100 millimeters. You can also use the swap control in the converter above to flip the direction instantly.
What is a millimeter?
Millimeter (mm) measures distance. A millimeter is one-thousandth of a meter. It is classified as a SI derived (metric prefix) unit.
What is a decimeter?
Decimeter (dm) is a unit of length.
Is the millimeter to decimeter conversion exact?
Yes. Both millimeter and decimeter are defined by fixed standards rather than physical artifacts, so the factor of 0.01 used above is exact to as many digits as you choose to display.
Where is the millimeter still used today?
Standard small/precision length unit worldwide, including in US engineering and manufacturing