Convert centimeters to inches in your browser. An inch is exactly 25.4 millimeters, fixed by international agreement in 1959.
in = cm ÷ 2.54
NIST SP 811 (2008), Appendix B.8 — inch (in) to meter (m) = 2.54 E−02
This is the conversion that shows up when buying things: screen diagonals, wheel sizes, waist measurements and paper formats are quoted in inches in some markets and centimeters in others. The inch is defined as exactly 25.4 millimeters, a number chosen in 1959 precisely so that both systems could agree without rounding.
in = cm ÷ 2.54
Because an inch is exactly 25.4 millimeters, it is exactly 2.54 centimeters. Dividing by that number is exact; multiplying by 0.3937 is not, and the error grows with the measurement.
Source: NIST SP 811 (2008), Appendix B.8 — inch (in) to meter (m) = 2.54 E−02
| centimeters | inches |
|---|---|
| 1 | 0.39370079 |
| 2.54 | 1 |
| 5 | 1.9685039 |
| 10 | 3.9370079 |
| 15 | 5.9055118 |
| 20 | 7.8740157 |
| 30 | 11.811024 |
| 50 | 19.685039 |
| 100 | 39.370079 |
| 170 | 66.929134 |
| 180 | 70.866142 |
A number that disagrees with its source is a defect, not a rounding preference.
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