How many centimeters are in an inch?
There are exactly 2.54 centimeters in an inch. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54.
The value of 2.54 centimeters per inch was agreed upon internationally in 1959, when English-speaking countries standardized their units. Before that, the inch varied very slightly between the United States and the United Kingdom, which caused problems in precise engineering and manufacturing.
Some useful conversions: 10 inches equals 25.4 centimeters, a 12-inch ruler is 30.48 centimeters long and a 30-centimeter ruler is about 11.8 inches. A person who is 170 centimeters tall is about 5 feet 7 inches. Screen sizes for TVs and phones are still usually given in inches, measured diagonally.
A quick estimate
For a rough mental conversion, you can think of an inch as about two and a half centimeters. One centimeter is about 0.39 inches, a little less than half an inch. Many rulers show both inches and centimeters on opposite edges, making comparison easy.
Did You Know?
Bicycle wheels and pipe sizes are often given in inches even in countries that use the metric system for most other measurements.