A conversion factor used to convert units of length expressed in the English system (i.e., inches) to a metric measurement (i.e., centimeters), as 1 inch equals 2.54 centimeters. Thus, to convert to centimeters, the number of inches is multiplied by 2.54 (i.e., a length that is 5 inches long would be converted as 5 x 2.54 = 12.7 centimeters). To convert to millimeters, the number of inches is multiplied by 25.4 (as there are 10 millimeters in a centimeter, and 25.4 millimeters in an inch). Thus, a 5-inch length would be converted as 5 x 25.4 = 127 millimeters.

To convert from metric to inches, the number of inches in one centimeter can be used. (See Metric-to-Inches Conversion.)