Convert centimeter to millimeter.

Convert centimeter (cm) to millimeter (mm). This is a fixed-ratio conversion — multiply the input by the factor below.

Formula

mm = cm × 10

Reference values

Things to watch for

• The international inch is exactly 25.4 mm (defined since 1959), so length conversions are exact, not approximations.
• Use mm for engineering drawings, cm for everyday measurements, m for room dimensions, km for distances.
• 1 mile = 1.609344 km (exact). Nautical miles are different: 1 nmi = 1852 m exactly (defined for nautical use).

What is a centimeter?

One centimeter equals exactly 10 millimeters or one-hundredth of a meter (1 cm = 0.01 m). Everyday measurements like clothing sizes, fabric, paper dimensions, and elementary-school rulers.

What is a millimeter?

One millimeter is exactly one-thousandth of a meter (1 mm = 0.001 m). It is the standard small-unit length in the SI metric system. Engineering drawings, machining tolerances, electronics dimensions, manufactured-part specifications, and rainfall measurement.

Everyday reference points for cm

Concrete examples often help when a unit doesn't have an intuitive feel. 15 cm is roughly the length of a standard pen; 30 cm is about the length of a 12-inch ruler; and 100 cm is one meter — roughly the height of a kitchen counter.

How to convert centimeter to millimeter

To convert a value from centimeter (cm) to millimeter (mm), apply the conversion factor shown in the formula above. The calculation is the same whether you do it by hand, in a spreadsheet, or with the live converter on this page.

Steps:

1. Take your input value in cm.
2. Apply the formula mm = cm × 10.
3. The result is your value in mm.

For repeated calculations, save the formula in a spreadsheet or use the live converter at the top of this page — it handles the math automatically and displays the result as you type.

Frequently asked questions

How do I convert cm to mm?

Apply the formula cm → mm shown above, or just type your value into the converter at the top of this page. The result updates instantly.

Which is bigger, cm or mm?

This depends on the conversion ratio in the formula. If the factor multiplied by your value gives a larger number, then mm is the smaller unit (so it takes more of them to express the same quantity). If the result is smaller, then mm is the larger unit.

When would I use cm versus mm?

Both units measure length, so the choice depends on context. Centimeter is typically used for engineering specs, construction, navigation, and everyday measurement; millimeter similarly. Most professional fields standardize on one or the other based on regional conventions or technical tradition.

How precise is this cm to mm conversion?

The conversion factor shown is the internationally defined exact value (or the best-published approximation if the relationship is irrational, like degrees-to-radians). The live converter on this page uses double-precision floating-point math, accurate to about 15 significant digits — far beyond any practical engineering need.

Is the conversion ratio exact, or an approximation?

Most unit conversions between SI metric units, and between SI and US customary units, have been formally defined as exact values since the 1959 international yard-pound agreement and subsequent SI redefinitions. Exceptions are unit pairs that involve irrational numbers (radians, e.g.) or empirical conversions (like food calories, which depend on temperature). When in doubt, consult the formula at the top of this page.

Related conversions

See also