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Length

Inches to Centimeters

1 inch = 2.54 cm exactly. Type whole inches, decimals or fractions such as 3 1/2 and read the length in centimeters.

Last updated:

Key Formula

1 in = 2.54 cm

1 cm ≈ 0.3937 in

cm

2.54

Need other units? Try the full unit converter →

Inches → Centimeters

Inches → Centimeters 1–10 in
incm
1 in2.54 cm
2 in5.08 cm
3 in7.62 cm
4 in10.16 cm
5 in12.70 cm
6 in15.24 cm
7 in17.78 cm
8 in20.32 cm
9 in22.86 cm
10 in25.40 cm
Inches → Centimeters 12–72 in
incm
12 in30.48 cm
15 in38.10 cm
18 in45.72 cm
20 in50.80 cm
24 in60.96 cm
30 in76.20 cm
36 in91.44 cm
48 in121.92 cm
60 in152.40 cm
72 in182.88 cm

How to convert inches to cm

cm = in × 2.54

Because 2.54 is an exact factor, the only rounding happens when you choose how many decimals to keep.

A 12-inch ruler

  1. 12 in × (2.54 cm / 1 in)
  2. the inch units cancel
  3. = 30.48 cm

3 1/2 inches

  1. Turn the fraction into a decimal: 3 + 1/2 = 3.5 in
  2. 3.5 × 2.54 = 8.89 cm

What is an inch?

The international inch is exactly 25.4 millimeters. The United States and several Commonwealth countries fixed this value together with the yard (0.9144 m) in the refinement that took effect on 1 July 1959; the inch is 1/36 of that yard.

Before 1959 the U.S. inch was slightly longer, about 25.400 050 8 mm, although the American Standards Association had already adopted the 25.4 mm inch in 1933. NIST's conversion table lists inch → meter as exactly 2.54 × 10⁻², which is where the factor 2.54 cm comes from.

Source: US Metric Association — Refinement of Values for the Yard and the Pound (retrieved 2026-09-29) / NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (retrieved 2026-09-29)

References

Where the 2.54 factor for inches to centimeters is defined.

NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science

NIST's conversion-factor tables; the length section gives inch → centimeter as 2.54, marked exact.

US Metric Association — Refinement of Values for the Yard and the Pound

Background on the 1959 change that made the U.S. inch exactly 25.4 mm.

FAQ

Exactly 2.54 cm. The inch has been defined as 25.4 mm since 1959, so no rounding is involved.

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