Convert Millimeters to Decimetres
1 millimeter is 0.01 dm. One millimeter is exactly 0.01 decimetres.
One millimeter is 0.01 decimetres. To convert millimeters to decimetres, multiply by 0.01; to go the other way, divide by 0.01 or multiply by 100. The factor is exact rather than rounded: it follows from NIST. One thousandth of a meter.
Factor checked against the defining standard · How we check
- Millimeters × 0.01
1 * 0.010.01 dm
1 millimeter in every length unit
| Unit | Value | Exact factor |
|---|---|---|
| inches | 0.03937007874 in | × 0.0393700787402 |
| feet | 0.003280839895 ft | × 0.00328083989501 |
| yards | 0.001093613298 yd | × 0.00109361329834 |
| miles | 0.0000006213711922 mi | × 0.000000621371192237 |
| millimeters (as entered) | 1 mm | — |
| decimetres | 0.01 dm | × 0.01 |
| centimeters | 0.1 cm | × 0.1 |
| meters | 0.001 m | × 0.001 |
| kilometers | 0.000001 km | × 0.000001 |
| nautical miles | 0.0000005399568035 nmi | × 0.000000539956803456 |
| micrometers | 1,000 µm | × 1,000 |
| nanometers | 1,000,000 nm | × 1,000,000 |
| thou | 39.37007874 thou | × 39.3700787402 |
Factors are entered by hand from NIST rather than derived from a units library, so the ones that terminate are exact rather than rounded.
The same converter answers this pair however it is written: millimetres to decimetres is the British spelling of the same units — the metre and the litre are spelled that way outside the United States and the quantity does not change.
How do you convert millimeters to decimetres? The converter and the working
- 1.Take the measurement in millimeters.
- 2.Multiply by 0.01 — that is how many decimetres fit in one millimeter.
- 3.To go back the other way, divide by 0.01, or multiply by 100.
Worked example: 25 millimeters to decimetres
- Formula
- mm × 0.01 = dm
- Arithmetic
- 25 × 0.01 = 0.25 dm
- Answer
- 25 mm = 0.25 dm
The factor is exact, so this figure is exact too — only the display is rounded.
Millimeters to decimetres conversion table
| Millimeters | Decimetres |
|---|---|
| 1 mm | 0.01 dm |
| 2 mm | 0.02 dm |
| 3 mm | 0.03 dm |
| 4 mm | 0.04 dm |
| 5 mm | 0.05 dm |
| 6 mm | 0.06 dm |
| 7 mm | 0.07 dm |
| 8 mm | 0.08 dm |
| 9 mm | 0.09 dm |
| 10 mm | 0.1 dm |
| 12 mm | 0.12 dm |
| 15 mm | 0.15 dm |
| 20 mm | 0.2 dm |
| 25 mm | 0.25 dm |
| 50 mm | 0.5 dm |
| 100 mm | 1 dm |
| 200 mm | 2 dm |
| 300 mm | 3 dm |
| 500 mm | 5 dm |
| 1000 mm | 10 dm |
| 2000 mm | 20 dm |
| 5000 mm | 50 dm |
| 10000 mm | 100 dm |
What is a millimeter?
One thousandth of a meter. The working unit of metric engineering drawings, which avoid decimals by using it throughout.
What is a decimetre?
A tenth of a metre. Rare in speech and unavoidable in definitions: the litre is a cubic decimetre, which is where the millilitre and the cubic centimetre meet.
How many decimetres are in a millimeter?
One millimeter is 0.01 decimetres, exactly. Going the other way, one decimetre is 100 millimeters. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every length unit here
The whole group — 13 units with their symbols and the size of each one in meters — is on the conversion index, along with every pair it makes. The table above already gives each of them relative to a millimeter.
Source: NIST — international yard and pound agreement (inch = 25.4 mm exactly)
Cite this page
- APA
- Rule Calculator. (2026). Convert Millimeters to decimetres. Rule Calculator. https://rulecalculators.com/convert/millimeter-to-decimeter
- MLA
- "Convert Millimeters to decimetres." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/millimeter-to-decimeter.
- Chicago
- Rule Calculator. "Convert Millimeters to decimetres." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/millimeter-to-decimeter.
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Questions people actually ask
- How many decimetres are in a millimeter?
- 0.01. A tenth of a metre. Rare in speech and unavoidable in definitions: the litre is a cubic decimetre, which is where the millilitre and the cubic centimetre meet.
- How do I convert decimetres back to millimeters?
- Divide by 0.01, or multiply by 100 — they are the same operation.
Other length conversions
Decimetres to millimeters — the same conversion the other way.