Inches to millimeters length units conversion factor is 25.4. To find out how many millimeters in inches multiply the inch value by 25.4.
1 Inch = 25.4 Millimeters
There are 25.4 millimeters in an inch, because for both imperial and US Customary measurement systems, one foot is defined as 30.48 centimeters (or 304.8 millimeters) exactly by an international agreements and there are 12 inches in a foot, that makes 304.8 / 12 = 25.4 mm in an inch.
For example, to find out how many millimeters there are in an inch and a half, multiply the inch value by the conversion factor, that makes 1.5 * 25.4 = 38.1 millimeters in 1.5 inches.
Inch is an imperial and US Customary measurement systems length unit. 1 inch equals to 25.4 millimeters and 2.54 centimeters. The abbreviation is "in".
Millimeter is a metric length unit and equal to one thousandth of a meter. It is used to measure small distances in engineering and machining. The abbreviation is "mm".