Why Is One Inch 2.54 CM?
Understand why one inch is exactly 2.54 centimeters and what that exact definition means.
An exact definition
In 1959, countries using the yard and pound agreed on an international yard equal to exactly 0.9144 meters. Because a yard contains 36 inches, one inch became exactly 0.0254 meters, or 2.54 centimeters.
Exact does not mean every result is short
The conversion factor is exact, but converting centimeters back to inches often creates repeating decimals. Displayed values are therefore commonly rounded.
Related measurement tools
Convert a value with the inches-to-cm converter, use the reverse centimeter converter, or compare common values in the inch-to-cm chart. Popular examples include 10 inches in cm and 12 inches in cm.
Browse the complete inch-to-cm chart →
Frequently asked questions
Is 2.54 cm an approximation?
No. The international inch is defined as exactly 2.54 centimeters.
When was the international inch standardized?
The current international definition was adopted in 1959.