Convert Inch to Millimeter

One in equals 25.4 mm. This converter allows you to easily convert between Inch and Millimeter in real time.

Formula

in × 25.4 = mm

Example: 1 in = 25.4 mm

What is Inch?

The inch is a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters. The word comes from the Latin "uncia," meaning one-twelfth, as there are 12 inches in a foot. Screen sizes for televisions, monitors, and smartphones are universally measured diagonally in inches. In plumbing and hardware, pipe diameters and bolt sizes are often specified in inches, even in countries that otherwise use the metric system.

What is Millimeter?

The millimeter is one-thousandth of a meter and is used wherever high precision is required. Engineers specify screw sizes, circuit board dimensions, and mechanical tolerances in millimeters. In meteorology, rainfall is measured in millimeters, with weather reports stating amounts like "20 mm of rain expected today." Paper thickness, smartphone dimensions, and dental measurements are also commonly expressed in millimeters.