| 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 |
| Millimeters (mm) | Centimeters (cm) |
|---|---|
| 12 | 1.2 |
| 15 | 1.5 |
| 20 | 2 |
| 25 | 2.5 |
| 30 | 3 |
| 40 | 4 |
| 50 | 5 |
| 60 | 6 |
| 75 | 7.5 |
| 100 | 10 |
Dividing by ten
A centimeter holds ten millimeters, so the conversion is a single move of the decimal point one place to the left: 85 mm is 8.5 cm and 6 mm is 0.6 cm. No rounding is ever needed, which is why metric lengths are so easy to change between.
To go from centimeters back to millimeters, move the point one place the other way: 3.2 cm is 32 mm.
Millimeters you meet often
- Rainfall is reported in millimeters: 25 mm of rain is 2.5 cm of water on flat ground.
- Camera lenses are named by focal length: a 50 mm lens has a focal length of 5 cm.
- Phones are usually 7 to 9 mm thick, under a centimeter.
- Beads and gemstones are sized in millimeters: an 8 mm bead is 0.8 cm across.
Which unit to write
Pick the unit that keeps numbers whole. Product sizes, bolts and wall thicknesses read best in millimeters; body measurements, fabric and furniture are usually written in centimeters. Converting is only needed when two sources disagree, and then cm to mm and this page share the same factor of 10.
NIST lists the metric prefixes in its SI prefix guide: milli is one thousandth and centi one hundredth of the base unit, so their ratio is exactly ten.
When you write a converted value, keep the precision you measured with. A part measured to the nearest millimeter, say 47 mm, becomes 4.7 cm, not 4.70 cm, because the extra zero would claim a precision you never had.
Clothing and shoe labels in metric countries sometimes mix both units, with foot length in millimeters and garment sizes in centimeters.
One millimeter in other length units
One millimeter in every other length unit on this site
- Centimeters0.1 cm
- Meters0.001 m
- Kilometers0.000001 km
- Inches0.039370079 in
- Feet0.0032808399 ft
- Yards0.0010936133 yd
- Miles6.2137119E-7 mi
Mm to cm questions
How many cm is 100 mm?
100 ÷ 10 = 10 cm.
What is 5 mm in centimeters?
5 mm is 0.5 cm, half a centimeter.
Why do some rulers only show millimeters?
Technical rulers and steel rules are often numbered every 10 mm without marking centimeters, because drawings use millimeters only. Each numbered mark is still one centimeter apart.
Is 1 mm smaller than 1/16 inch?
Yes. 1/16 in is 1.5875 mm, so a millimeter is about two thirds of a sixteenth.
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