About the MM to CM Converter
This mm to cm converter turns millimeters into centimeters by dividing by 10, and switches to centimeters-to-millimeters when you change the input unit. It also shows the length in meters and inches so you can cross-check against an imperial ruler.
Millimeters and centimeters appear side by side on rulers, rainfall reports, jewelry and ring sizes, screw and drill-bit sizes, camera specs, sewing patterns and medical measurements. Getting the decimal point in the right place is easy to fumble when you are switching between them, which is what this tool is for.
Both are SI units based on the meter: one centimeter is 10 millimeters, and one meter is 100 cm or 1,000 mm. The inch figure uses the exact definition 1 in = 25.4 mm.
With the default inputs, the centimeters is 2.5 cm. Change any value above to recalculate instantly.
How to use the mm to cm converter
- 1Enter the length.
- 2Choose millimeters or centimeters as the starting unit.
- 3Read centimeters and millimeters, plus meters and inches.
- 4Use the chart for common small measurements.
Formula and method
The prefix milli- means one thousandth and centi- means one hundredth, so a millimeter is 0.001 m and a centimeter is 0.01 m. One centimeter therefore contains exactly 10 millimeters: divide mm by 10 to get cm, or multiply cm by 10 to get mm.
In practice this just moves the decimal point one place — 47 mm is 4.7 cm, and 3.2 cm is 32 mm. Meters are mm ÷ 1,000, and inches are mm ÷ 25.4 because the inch is defined as exactly 25.4 mm.
- mm
- Length in millimeters
- cm
- Length in centimeters
Worked examples
25 mm screw
25 ÷ 10 = 2.5 cm. In inches, 25 ÷ 25.4 = 0.984 in — just under an inch.
17.5 cm phone length in mm
17.5 × 10 = 175 mm, which is 0.175 m.
3 mm of rain
3 ÷ 10 = 0.3 cm of rainfall, or about 0.12 inches.
Frequently asked questions
How many mm are in a cm?+
There are exactly 10 millimeters in one centimeter. On a metric ruler, the small marks between each numbered centimeter are millimeters.
How do I convert mm to cm?+
Divide by 10, which simply moves the decimal point one place to the left. For example, 85 mm = 8.5 cm and 4 mm = 0.4 cm.
How do I convert cm to mm?+
Multiply by 10, moving the decimal point one place to the right. For example, 2.3 cm = 23 mm.
Which is bigger, mm or cm?+
A centimeter is bigger — it is ten times the length of a millimeter. A standard credit card is about 0.76 mm thick, so a millimeter is a little more than that.
How many mm is an inch?+
One inch is exactly 25.4 mm, or 2.54 cm. That definition has been international since 1959.