How Many Millimeters in a Centimeter? (Quick Chart + Conversion)

1 centimeter equals 10 millimeters. Always, exactly, by definition. There are no fractions or rounding involved. The metric system is built on powers of 10.

Why 10?

The metric system uses base-10 prefixes. The base unit is the meter. Common length units:

• 1 meter equals 100 centimeters or 1,000 millimeters
• 1 centimeter (cm) equals 1/100 meter or 10 millimeters
• 1 millimeter (mm) equals 1/1,000 meter or 0.1 centimeter
• 1 decimeter equals 10 centimeters or 100 millimeters (rarely used in everyday speech)

The prefix centi- means "one hundredth"; milli- means "one thousandth." Both come from Latin numerals.

Quick Conversion Chart: CM to MM

How to Convert

CM to MM: multiply by 10. Examples: 3.2 cm becomes 32 mm; 7.5 cm becomes 75 mm; 0.4 cm becomes 4 mm.

MM to CM: divide by 10. Examples: 47 mm becomes 4.7 cm; 8 mm becomes 0.8 cm; 235 mm becomes 23.5 cm.

The shortcut: move the decimal point one place. Right for cm to mm, left for mm to cm.

Real-World Examples

• A standard pencil eraser is about 5 mm or 0.5 cm wide.
• A US dime is 17.9 mm or 1.79 cm diameter.
• A standard credit card is 85.6 mm or 8.56 cm wide.
• A new pencil is 190 mm or 19 cm long.
• A standard ruler is 300 mm or 30 cm long.

When to Use MM vs CM

Use millimeters when precision matters (engineering, jewelry, electronics, medical) or for objects smaller than 10 mm. Use centimeters for everyday measurements (clothing, paper, furniture) where 0.5 cm precision is enough.

Both are simultaneously available in our online ruler. Toggle between CM and MM with one tap.