The millimeter is a unit of length in the metric system. You can convert millimeters to inches in one of two ways: divide the number of millimeters by 25.4, or multiply the number of millimeters by 0.0394.

### Worked Example

Suppose you need to convert 51 millimeters to inches. You can divide 51 by 25.4, which equals approximately 2 inches. Alternatively, you may multiply 51 by 0.0394, which again produces about 2 inches. Depending on the degree of accuracy needed, you may opt to round your answer to different digits. For instance, if you convert 17 millimeters to inches, you obtain a result of about 0.669 inches. You might leave this answer as-is, or round it to 0.67 or even 0.7 inch.