Convert Millimeters (mm) to Centimeters (cm)

What Is a Millimeter?

The millimeter (mm) is a metric unit of length equal to one thousandth (1/1000) of a meter or 0.1 centimeters. It is the standard unit for precision measurements in engineering, manufacturing, electronics, jewelry, and medical imaging. Technical drawings and CNC machine specifications use millimeters.

What Is a Centimeter?

The centimeter (cm) is a metric unit equal to one hundredth (1/100) of a meter or 10 millimeters. It is the most common unit for everyday measurements — body height, clothing sizes, furniture dimensions, and screen sizes in metric countries.

Millimeters to Centimeters Formula

The conversion is exact by SI definition:

centimeters = millimeters ÷ 10 exact

Since 1 cm = 10 mm exactly, dividing by 10 gives the exact result. No rounding needed.

Worked Example

Convert 254 mm (exactly 10 inches) to centimeters:

1. Divide: 254 ÷ 10 = 25.4 cm

Quick Estimation

Just move the decimal 1 place left. No rounding needed. Examples: 5 mm = 0.5 cm, 35 mm = 3.5 cm, 150 mm = 15 cm.

Common Millimeters to Centimeters Conversions

When You Need This Conversion

• Engineering to everyday: Technical specs use mm (a bolt is 10 mm), but people think in cm for everyday context (1 cm ≈ fingernail width). Converting helps visualize sizes.
• Jewelry: Ring inner diameters are measured in mm (e.g., 18.2 mm = 1.82 cm). Gem sizes mix both units depending on the supplier.
• Medical: Tumor sizes are reported in mm on imaging (e.g., a 15 mm nodule = 1.5 cm), while patient-facing communication often uses cm.