How Many Millimeters in a Centimeter?

There are 10 millimeters in 1 centimeter. This is an exact relationship within the metric system, so you never have to round. To convert centimeters to millimeters, multiply by 10. To convert millimeters to centimeters, divide by 10. For example, 4 cm = 40 mm, and 85 mm = 8.5 cm.

The reason is built into the names. The prefix "centi" means one-hundredth of a meter, and "milli" means one-thousandth of a meter. Because a thousandth is ten times smaller than a hundredth, ten millimeters line up exactly with one centimeter every time.

Centimeters to Millimeters Chart

Each centimeter is simply the millimeter value with the decimal point moved one place. Use this chart for the most common values.

Reading a Ruler

A standard metric ruler makes the 10-to-1 ratio easy to see. The longest, numbered lines mark each centimeter. Between any two numbered lines you will find a set of shorter marks — those are the millimeters.

Count them and there are always 10 small divisions in a single centimeter. The slightly taller mark in the middle sits at the half-centimeter point, which is 5 mm. So if a pencil tip stops three small marks past the 6 cm line, it measures 6.3 cm, or 63 mm.

Metric Ladder

Millimeters and centimeters are two rungs on the same decimal ladder, where each step up is ten times larger than the one below it. Knowing the order lets you convert in your head:

• 1 mm = 0.1 cm = 0.001 m
• 10 mm = 1 cm = 0.01 m
• 1,000 mm = 100 cm = 1 m

Because every jump is a factor of 10, converting between metric length units is just a matter of shifting the decimal point. There are no awkward fractions the way there are when working with inches and feet.

For any value — including decimals and other length units — run it through our length converter for an instant, exact result.