The conversion factor
1 millimeter equals 0.03937 inches. Multiply your millimeters value by 0.03937 to get inches; divide to go back. For the reverse direction, use the inches to millimeters converter or the full length converter.
Where this conversion comes up
Mixing metric and imperial is a daily reality in travel, shipping, recipes, fitness apps, and spec sheets — this page gives the exact factor plus a scannable table for the values people actually need.