Home / Conversions / Length Converter / in to mm Inches to millimeters (in to mm) 1 in = 25.4 mm. Enter any value below to convert inches to millimeters instantly, or use the length converter for every other unit.
Maintained by Jairo Tunisse · Last updated October 5, 2026 · Editorial policy
1 in = 25.4 mm
mm = in × 25.4
Converted value 1 in = 25.4 mm 1 in = 25.4 mm
1 in = 0.0254 m (exact)
Result in Millimeters (mm) 25.4
Reverse factor 1 mm = 0.03937007874 in
Common length conversions 1 in 2.54 cm 1 ft 0.3048 m 1 yd 0.9144 m 1 mi 1.609344 km 1 nmi 1.852 km 1 m 3.280839895 ft 1 km 0.6213711922 mi 1 cm 0.3937007874 in
Inches to millimeters conversion table Inches to millimeters Inches (in) Millimeters (mm) 0.125 in 3.175 mm 0.25 in 6.35 mm 0.5 in 12.7 mm 0.75 in 19.05 mm 1 in 25.4 mm 2 in 50.8 mm 3 in 76.2 mm 6 in 152.4 mm 12 in 304.8 mm
The formula mm = in × 25.4
1 in = 0.0254 m (exact). 1 mm = 0.001 m. These are exact definitions, so the only rounding is in the displayed result (10 significant digits).
When you need it Inches to millimeters is common in machining, 3D printing and woodworking, where drawings mix fractional inches with metric parts. Multiply by 25.4. Converting fractions first to decimals (3/8 = 0.375) keeps the arithmetic simple.
More length converter conversions Frequently asked questions How do I convert inches to millimeters? Multiply the value in inches by 25.4 (or divide by 0.03937007874). For example, 0.75 in = 19.05 mm.
How many millimeters are in one inch? 1 in = 25.4 mm.
What is 1/2 inch in mm? Exactly 12.7 mm, so a 12 mm metric part is slightly smaller than a 1/2-inch one.
What is 3/8 inch in mm? 3/8 inch is 0.375 in, which is exactly 9.525 mm.
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Conversions use exact published unit definitions and are rounded to 10 significant digits for display. For legal metrology, trade or engineering work, confirm the governing standard.