Inches and centimeters
The inch is exactly 25.4 millimeters, one twelfth of a foot. Screen diagonals, wheel and tire sizes, pipe threads, and most US measurements of small objects use inches.
The centimeter is one hundredth of a meter (10 mm). Body height, clothing measurements, screen and paper sizes are commonly given in centimeters outside the US.
Worked example
Convert 12 in: 12 × 2.54 = 30.48, so 12 inches is 30.48 centimeters. Likewise 20 in = 50.8 cm.
Estimating in your head
Multiply by 2.5 for a quick figure; it is off by about 1.6%. For 12 in that gives 30 cm, against 30.48 exactly.
Going the other way
To convert centimeters to inches, divide by 2.54 (or multiply by 0.393700787402). The swap button between the boxes opens that page.
How this works
cm = in × 2.54
1 in = 0.0254 m and 1 cm = 0.01 m, both by definition, so the factor is their ratio: 2.54 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many centimeters are in a inch?
1 inch = 2.54 centimeters, exactly. The value follows from the unit definitions, so it never changes.
How do I convert inches to centimeters?
Multiply by 2.54. For example, 20 in × 2.54 = 50.8 cm.
What is 100 in in centimeters?
100 in = 254 cm. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Federal Register 59-5442 (1959) — Refinement of values for the yard and the pound
- Wikipedia — Conversion of units of length
Reviewed Oct 17, 2026 · test vectors fixtures/units/length/inches-to-cm/