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The metric-to-imperial length conversion you use every day
From screen diagonals to clothing dimensions and architectural drawings, centimeters and inches need to talk to each other constantly. This calculator converts any cm value to inches instantly using the exact definition: 1 inch = 2.54 cm.
The formula
in = cm ÷ 2.54
- cm — the length in centimeters.
- in — the equivalent length in inches.
- 2.54 — the exact conversion factor (1 in = 2.54 cm, per the 1959 international agreement).
Alternatively: in = cm × 0.3937 (the reciprocal of 2.54).
Worked example
Using the default of 5 cm:
- Divide by 2.54: 5 ÷ 2.54 = 1.9685…
- Round to 2 decimal places: 1.97″.
So 5 cm ≈ 1.97 inches.
Conversion table
| CM | Inches |
|---|---|
| 1 | 0.394 |
| 2 | 0.787 |
| 5 | 1.969 |
| 10 | 3.937 |
| 15 | 5.906 |
| 20 | 7.874 |
| 25 | 9.843 |
| 30 | 11.811 |
| 50 | 19.685 |
| 100 | 39.370 |
History & standards
The centimeter is 1/100 of the meter, the SI base unit of length defined since 1983 by the speed of light. The inch traces back to Roman and Anglo-Saxon units (the “uncia”, or twelfth of a foot). The modern, exact value — 1 in = 25.4 mm = 2.54 cm — was fixed by the 1959 International Yard and Pound Agreement between the US, UK, Australia, Canada, New Zealand and South Africa.
Common applications
- Screen sizes. Monitors and TVs are rated by diagonal in inches; product specs often list the cm equivalent.
- Clothing. EU garment sizing uses cm for waist and inseam; US sizing uses inches.
- Construction. Architects work in meters/cm; US contractors need inch equivalents for fittings.
- Medical imaging. Tumor and organ measurements are recorded in cm; some reporting standards require inches.
- Photography. Print dimensions are quoted in inches in the US; cm elsewhere.
Reverse conversion
To convert inches to cm, multiply by 2.54: cm = in × 2.54. Use the inches to cm calculator for instant results in the other direction.
Limitations & gotchas
- Decimal vs. fractional inches. The calculator returns decimal inches. Convert to fractions (e.g. 3/8″) manually if your application requires it.
- Display rounding. Results are shown to 2–4 decimal places. The underlying arithmetic uses the exact value 2.54.
- US survey foot (deprecated). The old US survey inch (slightly different) was retired by NIST in 2023. The international inch is now the sole US standard.
Sources & references
- NIST SP 811, Guide for the Use of the International System of Units (SI).
- BIPM, The International System of Units (SI), 9th edition.
- 1959 International Yard and Pound Agreement.
FAQs
Divide the centimeter value by 2.54. For example, 5 cm ÷ 2.54 = 1.969 inches. Alternatively, multiply by 0.3937 (the reciprocal of 2.54). Both routes use the exact definition: 1 inch = 2.54 cm.
Exactly 0.3937 inches (1 ÷ 2.54). This follows from the 1959 International Yard and Pound Agreement, which set 1 inch = 25.4 mm = 2.54 cm as an exact definition.
10 cm ÷ 2.54 = 3.937 inches, often rounded to 3.94″.
30 cm ÷ 2.54 = 11.811 inches — very close to a standard 12-inch ruler.
A centimeter is 1/100 of a meter in the SI metric system. An inch is 1/12 of a foot in the imperial system. The two are related by the exact definition 1 in = 2.54 cm, so 1 cm is about 40% of an inch (0.3937″).
Yes. TV and monitor sizes are always quoted as the diagonal in inches. If a product listing gives the diagonal in cm, divide by 2.54 to get the equivalent inch size. For example, a 55″ screen is 55 × 2.54 = 139.7 cm.