To convert mm to inches you need to divide the value in mm by 25.4 as there are this many millimeters in an inch. For example, suppose you have a length of 100 millimeters and you want to convert it to inches: divide 100 by 25.4 which gives approximately 3.937 inches. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.