Because an inch is 25.4 millimetres long, 10 millimetres equals 0.3937 inches, or slightly more than one-third of an inch. In the metric system, 2.54 cm is another typical equivalent of one inch.
Because one millimetre equals 0.1 centimetre, ten millimetres equal one centimetre. Simply divide one centimetre by 2.54 to get the equivalent in inches. Within the metric system, converting is usually simple and usually involves changing a decimal point. For example, 0.1 decimeters and 0.01 metres are equal to 10 millimetres. Converting between the metric and the US systems is more difficult and frequently necessitates the use of mixed numbers.