Quick Answer: Inches to Centimeters
One inch equals 2.54 centimeters (1 in = 2.54 cm).
Conversely, 1 cm ≈ 0.3937 in.
Formula: cm = in × 2.54
Worked examples
- 1 in = 2.54 cm
- 2 in = 5.08 cm
- 3 in = 7.62 cm
Method and limitations
Multiply inches by 2.54. The international inch is exactly 2.54 cm (25.4 mm), fixed by the 1959 international yard and pound agreement. The factor is exact, so the only rounding is in how precisely the inch value was measured. Calculations use full-precision constants; answers in this box are rounded for readability (≈ marks a rounded value) and the calculator shows up to 9 significant figures.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
Multiply inches by 2.54. The international inch is exactly 2.54 cm (25.4 mm), fixed by the 1959 international yard and pound agreement. The factor is exact, so the only rounding is in how precisely the inch value was measured.
Complete Guide to Inches to Centimeters Conversion
What is an inch?
The inch (in, ″) is 1/12 of a foot and 1/36 of a yard. Since 1959 it has been defined as exactly 25.4 mm.
What is a centimeter?
The centimeter (cm) is 1/100 of a meter, the SI base unit of length.
How the Conversion Works
cm = in × 2.54. Because the factor is exact, report the result with the same precision as the original measurement — a tape reading of 12 in is 30.5 cm, not 30.48000 cm unless the 12 in was itself that precise.
Step-by-Step Conversion Guide
Follow these steps to convert inches to centimeters manually:
Start with your value in inches
Example: You want to convert 3 in
Apply the conversion formula
Use the formula: cm = in × 2.54
Calculate the result
3 in = 7.62 cm
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
Multiply by 2.5 and add a little: 10 in ≈ 25 cm (exact 25.4). 4 in ≈ 10 cm is a handy anchor.
Common Conversions
| Inches (in) | Centimeters (cm) | Centimeters → Inches |
|---|---|---|
| 1 in | 2.54 | 1 cm = 0.393701 in |
| 2 in | 5.08 | 2 cm = 0.787402 in |
| 3 in | 7.62 | 3 cm = 1.1811 in |
| 4 in | 10.16 | 4 cm = 1.5748 in |
| 5 in | 12.7 | 5 cm = 1.9685 in |
| 6 in | 15.24 | 6 cm = 2.3622 in |
| 10 in | 25.4 | 10 cm = 3.93701 in |
| 12 in | 30.48 | 12 cm = 4.72441 in |
| 24 in | 60.96 | 24 cm = 9.44882 in |
| 36 in | 91.44 | 36 cm = 14.1732 in |
| 48 in | 121.92 | 48 cm = 18.8976 in |
| 72 in | 182.88 | 72 cm = 28.3465 in |
| 100 in | 254 | 100 cm = 39.3701 in |
Popular Inches to Centimeters Conversions
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When You'll Need This Conversion
Product and screen dimensions
Read US listings given in inches against a metric space or specification.
Matching a metric specification
Check whether an inch-dimensioned part fits a drawing or opening given in cm.
Pro Tips for Accurate Conversions
Fractions first
Turn fractional inches into decimals before converting: 3/8 in = 0.375 in = 0.9525 cm.
Common Mistakes to Avoid
Converting feet-and-inches as a decimal
5.10 is not 5 ft 10 in; 5 ft 10 in is 5.833 ft.
Use total inches: (5 × 12) + 10 = 70 in = 177.8 cm.
Frequently Asked Questions
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.