Convert millimeter to centimeter.

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

Formula

cm = mm × 0.1

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 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.

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.

Real-world examples of mm

If the unit feels abstract, comparing it to known objects often helps.

• 10 mm — about the diameter of a pencil.
• 25 mm — about the width of a US quarter.
• 100 mm — roughly the length of a credit card.

How to convert millimeter to centimeter

To convert a value from millimeter (mm) to centimeter (cm), 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 mm.
2. Apply the formula cm = mm × 0.1.
3. The result is your value in cm.

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 mm to cm?

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

Which is bigger, mm or cm?

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

When would I use mm versus cm?

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

How precise is this mm to cm 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