Convert cm to mm
1 centimeter = 10 millimeters. Multiply centimeters by 10 to get millimeters; divide millimeters by 10 to go back.
Centimeters to millimeters conversion table
How to convert centimeters to millimeters
Take the value in centimeters.
10 cm
Multiply by 10.
10 × 10
Round to the precision you need.
= 100 mm
The centimeter and the millimeter are both defined in terms of the metre and the kilogram, so this factor is exact, not an approximation.
Table of Contents
Centimetres to millimetres
A centimetre is one hundredth of a metre and a millimetre is one thousandth, so a centimetre contains exactly ten millimetres: 1 cm = 10 mm. To convert, multiply the centimetres by 10, which moves the decimal point one place to the right. 2.5 cm is 25 mm, 0.8 cm is 8 mm, and 30 cm is 300 mm. The factor is exact, so a measurement loses nothing when it changes unit.
Why technical work prefers millimetres
Drawings, machine parts, screws and 3D-printing files are dimensioned in millimetres so that most values are whole numbers and decimals stay rare. A bolt described as M8 is 8 mm across; a 12.7 mm socket is half an inch. Everyday measurements such as clothing and paper sizes stay in centimetres because the numbers are shorter to say. A ruler shows both: the numbered marks are centimetres and the small divisions are millimetres.
Worked examples
A 15 cm phone is 150 mm long. A 0.5 cm gap is 5 mm. A4 paper is 21 cm by 29.7 cm, which is 210 mm by 297 mm. To go back, divide millimetres by 10: 45 mm is 4.5 cm.
What is a centimeter?
A centimeter is a unit of length in the metric system, equal to one-hundredth of a meter or 0.01 meters.
What is a millimeter?
A millimeter is a unit of length in the metric system, equal to one-thousandth of a meter or 0.001 meters.
Common centimeters to millimeters conversions
These are the values people actually search for. Any other number works in the converter above; only these pages are listed for search engines.