To convert inches to centimeters (in to cm), multiply by 2.54. 1 inch equals 2.54 cm, about 30% of a credit card's long edge.
| inches | centimeters |
|---|---|
| 1 inch | 2.54 cm |
| 2 inches | 5.08 cm |
| 5 inches | 12.7 cm |
| 10 inches | 25.4 cm |
| 25 inches | 63.5 cm |
| 50 inches | 127 cm |
| 100 inches | 254 cm |
| 250 inches | 635 cm |
| 500 inches | 1,270 cm |
| 1000 inches | 2,540 cm |
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.
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.
An inch is defined as exactly 25.4 millimetres, agreed internationally in 1959. This conversion is exact, not rounded.
For a quick estimate, multiply by 2.5. 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 2.54000 when it matters.
The reverse factor is 0.394, so one centimeter is that many inches. Two decimal places is plenty for most purposes, and three is more than a tape measure can justify.
To anchor the scale: 1 inch is about 2.54 cm.