Convert Decimetres to Millimeters
1 decimetre is 100 mm. One decimetre is exactly 100 millimeters.
One decimetre is 100 millimeters. To convert decimetres to millimeters, multiply by 100; to go the other way, divide by 100 or multiply by 0.01. The factor is exact rather than rounded: it follows from NIST. A tenth of a metre.
Factor checked against the defining standard · How we check
- Decimetres × 100
1 * 100100 mm
1 decimetre in every length unit
| Unit | Value | Exact factor |
|---|---|---|
| inches | 3.937007874 in | × 3.93700787402 |
| feet | 0.3280839895 ft | × 0.328083989501 |
| yards | 0.1093613298 yd | × 0.109361329834 |
| miles | 0.00006213711922 mi | × 0.0000621371192237 |
| millimeters | 100 mm | × 100 |
| decimetres (as entered) | 1 dm | — |
| centimeters | 10 cm | × 10 |
| meters | 0.1 m | × 0.1 |
| kilometers | 0.0001 km | × 0.0001 |
| nautical miles | 0.00005399568035 nmi | × 0.0000539956803456 |
| micrometers | 100,000 µm | × 100,000 |
| nanometers | 100,000,000 nm | × 100,000,000 |
| thou | 3,937.007874 thou | × 3,937.00787402 |
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: decimetres to millimetres 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 decimetres to millimeters? The converter and the working
- 1.Take the measurement in decimetres.
- 2.Multiply by 100 — that is how many millimeters fit in one decimetre.
- 3.To go back the other way, divide by 100, or multiply by 0.01.
Worked example: 25 decimetres to millimeters
- Formula
- dm × 100 = mm
- Arithmetic
- 25 × 100 = 2,500 mm
- Answer
- 25 dm = 2,500 mm
The factor is exact, so this figure is exact too — only the display is rounded.
Decimetres to millimeters conversion table
| Decimetres | Millimeters |
|---|---|
| 1 dm | 100 mm |
| 2 dm | 200 mm |
| 3 dm | 300 mm |
| 4 dm | 400 mm |
| 5 dm | 500 mm |
| 6 dm | 600 mm |
| 7 dm | 700 mm |
| 8 dm | 800 mm |
| 9 dm | 900 mm |
| 10 dm | 1,000 mm |
| 12 dm | 1,200 mm |
| 15 dm | 1,500 mm |
| 20 dm | 2,000 mm |
| 25 dm | 2,500 mm |
| 50 dm | 5,000 mm |
| 100 dm | 10,000 mm |
| 200 dm | 20,000 mm |
| 300 dm | 30,000 mm |
| 500 dm | 50,000 mm |
| 1000 dm | 100,000 mm |
| 2000 dm | 200,000 mm |
| 5000 dm | 500,000 mm |
| 10000 dm | 1,000,000 mm |
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.
What is a millimeter?
One thousandth of a meter. The working unit of metric engineering drawings, which avoid decimals by using it throughout.
How many millimeters are in a decimetre?
One decimetre is 100 millimeters, exactly. Going the other way, one millimeter is 0.01 decimetres. 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 decimetre.
Source: NIST — international yard and pound agreement (inch = 25.4 mm exactly)
Cite this page
- APA
- Rule Calculator. (2026). Convert Decimetres to millimeters. Rule Calculator. https://rulecalculators.com/convert/decimeter-to-millimeter
- MLA
- "Convert Decimetres to millimeters." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/decimeter-to-millimeter.
- Chicago
- Rule Calculator. "Convert Decimetres to millimeters." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/decimeter-to-millimeter.
The date is when the figures on this page were last checked against their source, not the day you opened it. Add your own access date if your style needs one.
Questions people actually ask
- How many millimeters are in a decimetre?
- 100. One thousandth of a meter. The working unit of metric engineering drawings, which avoid decimals by using it throughout.
- How do I convert millimeters back to decimetres?
- Divide by 100, or multiply by 0.01 — they are the same operation.
Other length conversions
Millimeters to decimetres — the same conversion the other way.