Since there are 25.4 millimetres in an inch, 10 millimetres is equal to 0.3937 inches, or a little more than one-third of an inch. In the metric system, 2.54 centimetres is often used to equal an inch.
Since 1 millimetre is equal to 0.1 centimetres, 10 millimetres is equal to 1 centimetre. To find out how many inches 1 centimetre is, you just need to divide 1 by 2.54. Most of the time, converting within the metric system is easy and can be done by moving a decimal point. For example, 10 millimetres is the same as 0.1 decimeters and 0.01 metres. Converting between the metric system and the system used in the United States is harder and often requires mixed numbers.