Millimeters to Centimeters
Ten millimeters make one centimeter, so divide millimeters by 10, moving the decimal point one place left: 35 mm is 3.5 cm and 297 mm is 29.7 cm.
1 millimeter = 0.1 centimeters
1 mm = 0.1 cm · multiply by 0.1
Who measures in millimeters
Engineers, carpenters and manufacturers almost always work in millimeters. Technical drawings across Europe and Asia give every dimension in millimeters without writing the unit, because a single unit removes the risk of mixing scales. Consumers, by contrast, tend to think in centimeters, so a cabinet drawn as 600 mm wide is described in a shop as 60 cm.
Weather is another field. Rain is measured in millimeters, while snow depth is usually given in centimeters, and as a rough rule 10 mm of rain falls as about 10 cm of fresh snow, though wet and dry snow vary a lot. Jewelers use millimeters for ring sizes, which are based on inner diameter or circumference: an inner diameter of 17.3 mm is 1.73 cm.
How to convert millimeters to centimeters
cm = mm × 0.1
1 mm = 0.1 cm
25 mm × 0.1 = 2.5 cm
- Start with the value in millimeters.
- Multiply it by 0.1.
- Round the result to the precision the job needs: whole numbers for everyday use, more decimals for engineering or recipes.
Photo and document sizes
ID photos are usually specified in millimeters. The common passport format of 35 × 45 mm is 3.5 × 4.5 cm, and a 2 × 2 in US photo is 50.8 × 50.8 mm, or 5.08 cm square. When an editor asks for the size in centimeters, divide by 10; you can then resize the image in centimeters at the print resolution you need.
Camera lenses are the exception that stays in millimeters. A 50 mm lens is never called a 5 cm lens, because focal length is conventionally written in millimeters worldwide.
Millimeters in centimeters, and back
Rounded to six significant digits. Change any value in the converter above for an exact figure.
| Millimeters (mm) | Centimeters (cm) |
|---|---|
| 1 | 0.1 |
| 2 | 0.2 |
| 3 | 0.3 |
| 4 | 0.4 |
| 5 | 0.5 |
| 6 | 0.6 |
| 7 | 0.7 |
| 8 | 0.8 |
| 9 | 0.9 |
| 10 | 1 |
| 12 | 1.2 |
| 15 | 1.5 |
| 20 | 2 |
| 25 | 2.5 |
| 30 | 3 |
| 40 | 4 |
| 50 | 5 |
| 60 | 6 |
| 70 | 7 |
| 75 | 7.5 |
| 80 | 8 |
| 90 | 9 |
| 100 | 10 |
| Centimeters (cm) | Millimeters (mm) |
|---|---|
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 40 |
| 5 | 50 |
| 6 | 60 |
| 7 | 70 |
| 8 | 80 |
| 9 | 90 |
| 10 | 100 |
| 12 | 120 |
| 15 | 150 |
| 20 | 200 |
| 25 | 250 |
| 30 | 300 |
| 40 | 400 |
| 50 | 500 |
| 60 | 600 |
| 70 | 700 |
| 75 | 750 |
| 80 | 800 |
| 90 | 900 |
| 100 | 1,000 |
Getting the decimal right
Since there are only ten millimeters in a centimeter, the decimal moves one place, not two: 5 mm is 0.5 cm, and 0.5 mm is 0.05 cm. Dividing by 100 by mistake gives answers ten times too small. For the reverse, see centimeters to millimeters.
Frequently asked questions
- How many cm is 1 mm?
- 1 mm is 0.1 cm, a tenth of a centimeter.
- What is a 35 × 45 mm passport photo in centimeters?
- It is 3.5 × 4.5 cm. Many countries, including the UK and most of the EU, use this size.
- Is 15 mm of rain a lot?
- 15 mm is 1.5 cm of water over the ground in a day, which counts as moderate to heavy rain in most climates.
- Why are engineering drawings in millimeters instead of centimeters?
- Using one small unit throughout avoids decimals in most dimensions and makes mixing units impossible, so ISO drawing standards default to millimeters.