The exact conversion factor
One international inch is exactly 2.54 centimeters. This is a defined relationship, not a rounded estimate.
Multiply inches by 2.54 to get centimeters. Divide centimeters by 2.54 to return to inches.
A practical example
A 12-inch measurement is 30.48 centimeters because 12 × 2.54 = 30.48. Keep extra decimal places during calculation and round only the final displayed result.
Avoid common mistakes
Do not confuse decimal inches with inch fractions. Convert a fraction such as 3/8 to its decimal value before multiplying. For precision work, record the tolerance of the original measurement as well as the converted number.