How to convert millimeters to inches

Step-by-step explanation of how to convert millimeters to inches, with formulas, worked examples, and a free online calculator.

Millimeters and inches are both used for small precision measurements. Millimeters are metric, common in engineering, machining, and most countries. Inches are Imperial, common in the United States. One inch equals exactly 25.4 millimeters. To convert mm to inches, divide by 25.4. For example, 50 mm ÷ 25.4 = 1.969 inches. To convert inches to mm, multiply by 25.4. This conversion comes up frequently in 3D printing, CNC machining, photography filter sizes, and watch face diameters.