cm to Inches Converter
Convert centimeters to inches for US product sizing, height, and measurement reference.
How It Works
Formula: cm to in = value × 0.393700787
Example: 30 cm = 11.811024 in
Note: 1 centimeter equals 0.3937 inches, derived from the exact definition 1 inch = 2.54 cm.
Common Uses
Quick Conversion Table
| cm | in |
|---|---|
| 1 | 0.3937 |
| 5 | 1.9685 |
| 10 | 3.937 |
| 50 | 19.685 |
| 100 | 39.3701 |
| 500 | 196.8504 |
| 1000 | 393.7008 |
Rounding Rule
Rounded to 4 decimal places
Error Margin
±0.0001 in
Precision Guidance
For sizing, round to 2 decimal places. For rough estimates, round to the nearest inch.
Common Mistakes
Do not estimate 1 cm as half an inch. The correct value is 0.3937 inches.
Frequently Asked Questions
What is 30 cm in inches?
30 cm equals 11.811 inches using the conversion 1 cm = 0.3937 in.
How do I convert cm to inches?
Multiply the centimeter value by 0.3937, or divide by 2.54.
Is 1 cm half an inch?
No, 1 cm is about 0.3937 inches. Half an inch is about 1.27 cm.
How accurate is this?
Exact by the international inch definition (1 in = 2.54 cm), accurate to 4 decimal places.
Deep Dive Guide
CM to Inches: Complete Conversion Guide for US Measurements
Convert cm to inches with the exact 0.3937 factor. Our guide covers product specs, clothing sizes, and travel for US readers.
Read Full Guide →More Converters You May Like
5 Feet to Meters Converter
Convert 5 feet to meters for US height and furniture measurement.
6 Feet to Meters Converter
Convert 6 feet to meters for US building and height data.
5'7'' to Meters Converter
Convert 5 feet 7 inches to meters - the average US adult height.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 inch (in) = 25.4 millimetres (exact)
- EXACT1 foot (ft) = 0.3048 metres (exact, 12 in)
- EXACT1 yard (yd) = 0.9144 metres (exact, 3 ft)
- EXACT1 mile (mi) = 1609.344 metres (exact, 5280 ft)
- EXACT1 centimetre (cm) = 0.01 metre (definition)
Common Pitfalls & How to Avoid Them
US survey foot is deprecated
The old US survey foot (0.304800609601 m) was retired in 2023 in favor of the international foot (0.3048 m). Modern conversions use the international foot; mixing them drifts over long distances.
Inches vs. centimetres for screens
Display and wheel sizes are often rounded to the nearest convenient number; a "27-inch" monitor is nominal, not a precise 68.58 cm panel.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
- BIPM (International Bureau of Weights and Measures) — SI Brochure — The International System of Units (9th edition)
Last Updated 2026 | This converter was reviewed for accuracy