To convert centimeters to inches (cm to in), multiply by 0.3937. 1 centimeter equals 0.3937 in, about 1.7 times as much as a grain of rice.
| centimeters | inches |
|---|---|
| 1 centimeter | 0.3937 in |
| 2 centimeters | 0.7874 in |
| 5 centimeters | 1.9685039 in |
| 10 centimeters | 3.9370079 in |
| 25 centimeters | 9.8425197 in |
| 50 centimeters | 19.685039 in |
| 100 centimeters | 39.370079 in |
| 250 centimeters | 98.425197 in |
| 500 centimeters | 196.85039 in |
| 1000 centimeters | 393.70079 in |
Definition: 1/100 of a meter - the "centi" prefix doing the same job it does in "century" or "cent."
History: Introduced alongside the meter itself during the French Revolution's metric overhaul, the centimeter was designed from the start to be a convenient, everyday-sized subdivision - a meter is often too big and a millimeter too small for describing things like a person's height or a book's thickness.
Current use: Height, everyday object sizes, and fabric measurements across most of the world; also the standard unit doctors use internationally for body measurements.
Definition: 1/12 of a foot, or exactly 25.4 millimeters.
History: The Romans had the "uncia" - one-twelfth of their foot, the same root word that gives us "ounce" today. Centuries later, medieval England needed something more practical and checkable than "one twelfth of a foot," so a 1308 statute under King Edward I defined an inch as the length of three grains of barley, dry and round, laid end to end - a definition ordinary people could actually verify for themselves without a ruler.
Current use: Screen sizes, paper formats, pipe diameters, and everyday measurements across the US, UK, and other imperial-leaning countries.
An inch is defined as exactly 25.4 millimetres, so this factor is exact by definition rather than measured.
For a quick estimate, multiply by 0.4. That is off by about 1.6%, which is fine for a rough figure and not fine for anything you are paying for or building to. Use the exact factor of 0.393701 when it matters.
Going the other way, one inch is 2.54 cm, which is usually the easier direction to work in. Because the forward factor is small, watch the decimal place rather than the digits: a factor-of-ten slip is the common error, not a rounding one.
To anchor the scale: 5 centimeters is about 1.97 in.