Convert Centimeters (cm) to Millimeters (mm)
1 centimeter equals 10 millimeters.
Centimeter to Millimeter Converter
What Is a Centimeter?
The centimeter (cm) is a metric unit of length equal to one hundredth (1/100) of a meter or 10 millimeters. It is widely used for body measurements (height, waist), clothing sizes, screen dimensions, and everyday object measurements in most countries outside the US.
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 work — engineering drawings, jewelry sizing, bolt specifications, paper thickness, and medical measurements like tumor sizes.
Centimeters to Millimeters Formula
The conversion is exact by SI definition:
millimeters = centimeters × 10 exact
The relationship is exact because both are decimal subdivisions of the meter: 1 cm = 10 mm, 1 m = 100 cm = 1,000 mm.
Worked Example
Convert 2.5 cm (roughly the diameter of a US quarter coin) to millimeters:
- Multiply: 2.5 × 10 = 25 mm
Quick Estimation
Just add a zero — or move the decimal 1 place right. No rounding needed. Examples: 0.5 cm = 5 mm, 3 cm = 30 mm, 15 cm = 150 mm.
Common Centimeters to Millimeters Conversions
| Centimeters | Millimeters | Context |
|---|---|---|
| 0.1 cm | 1 mm | Thickness of a credit card |
| 0.5 cm | 5 mm | Pencil diameter / small bead |
| 1 cm | 10 mm | Width of a fingernail |
| 2 cm | 20 mm | Width of a US nickel coin |
| 2.54 cm | 25.4 mm | Exactly 1 inch |
| 5 cm | 50 mm | Standard matchbox width |
| 10 cm | 100 mm | Width of a smartphone |
| 15 cm | 150 mm | Standard pen length |
| 30 cm | 300 mm | Standard ruler / 1 foot ≈ 30.48 cm |
When You Need This Conversion
- Engineering drawings: Technical specifications use mm for precision. A part measuring 3.5 cm on a sketch = 35 mm in the machine shop specification.
- Jewelry: Ring sizes, gem dimensions, and chain widths are specified in mm. A 1.8 cm (18 mm) ring inner diameter corresponds to approximately US ring size 8.
- 3D printing and CNC: Machine tolerances are in mm. A design measured at 7.5 cm = 75 mm, with typical tolerances of ±0.1 mm.
Frequently Asked Questions
How many millimeters are in a centimeter?
Exactly 10 millimeters. This is an exact metric definition.
How do I convert cm to mm?
Multiply by 10 — or move the decimal 1 place to the right. Example: 4.5 cm = 45 mm.
How many mm is 1 inch?
Exactly 25.4 mm (= 2.54 cm). This has been the international standard since 1959.
How do I convert mm back to cm?
Divide by 10. Example: 35 mm = 3.5 cm. Move the decimal 1 place left.
Common Centimeter to Millimeter Conversions
| Centimeter | Millimeter | Actions |
|---|---|---|
| 1 centimeter | 10 millimeters | |
| 2 centimeters | 20 millimeters |
| Centimeter | Millimeter | Actions |
|---|---|---|
| 5 centimeters | 50 millimeters | |
| 10 centimeters | 100 millimeters |
Centimeters to millimeters Conversion Table
Reference table with common centimeters to millimeters conversions. All values calculated with high precision.
Centimeters to Millimeters Table
1 to 100000
Millimeters to Centimeters Table
10 to 1000000
Looking for the reverse? Convert Millimeter to Centimeter
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- Sq Meters to Sq Feet — Area uses squared length units
