Centimeters to Millimeters (cm to mm)

How to convert centimeters to millimeters

Multiply the centimeters by 10:

millimeters = centimeters × 10

Multiplying by 10 moves the decimal point one place to the right: 1.5 cm = 15 mm, 0.3 cm = 3 mm, 12.7 cm = 127 mm. To go the other way, divide millimeters by 10.

Because millimeters are whole numbers for most everyday sizes, drawings, product specs and medical reports often use them instead of centimeters with a decimal.

Centimeters to millimeters chart

To convert a list of measurements, open Convert a list of values and paste the centimeters one per line.

Reading a metric ruler

A metric ruler is numbered in centimeters, with ten small marks between each number. Each small mark is 1 millimeter; the slightly longer mark in the middle is 5 mm.

• A pencil line ending 3 small marks past the 7 is 7.3 cm, or 73 mm.
• The half-way mark between 4 and 5 is 4.5 cm, or 45 mm.
• A 30 cm ruler is 300 mm long.

Reading the number of millimeters straight off the ruler avoids decimal slips.

Everyday sizes in millimeters

Many standard sizes are defined in millimeters, so converting centimeters to millimeters is often the step before checking a specification:

Jewelry widths, camera lens focal lengths, bolt and drill sizes, and rainfall totals are also given in millimeters. When a listing mixes the two units — a necklace “45 cm long, 3 mm wide” — convert both to millimeters (450 × 3 mm) to compare them directly.

Millimeters and inches

The result shows each length in inches as well. A millimeter is about 1/25 of an inch, and 25.4 mm is exactly one inch — so 2.54 cm is one inch, and 10 cm is 3.94 in. For inches with fractions to 1/64, use mm to inches; for centimeters to inches, cm to inches; for meters, cm to meters.