**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 or use the converter.

**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**".