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1 Inch to Millimeters

1 inch is 25.4 millimeters. See the step-by-step breakdown and reference table below, or try a different value in the calculator.

1 in = 25.4 mm
in × 25.4 = mm
Try: 2 in to mm 6 in to mm
1 in is also
1 in = 0.0000254 km 1 in = 0.0000157828 mi 1 in = 0.0254 m 1 in = 0.0833 ft 1 in = 2.54 cm 1 in = 0.0278 yd
in
25.4 mm

Step-by-Step Calculation

in × 25.4 = mm
  1. Start with 1 in
  2. Multiply by 25.4: 1 × 25.4 = 25.4
  3. Result: 1 in = 25.4 mm

This conversion factor (25.4) is the same for every inch to millimeter calculation.

Inch to Millimeter Conversion Table

Inches (in) Millimeters (mm)
1 in 25.4 mm
2 in 50.8 mm
5 in 127 mm
10 in 254 mm
15 in 381 mm
20 in 508 mm
25 in 635 mm
50 in 1,270 mm
75 in 1,905 mm
100 in 2,540 mm
250 in 6,350 mm
500 in 12,700 mm
1,000 in 25,400 mm
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Frequently Asked Questions

1 inch equals 25.4 millimeters.
The formula is: in × 25.4 = mm. See the in to mm formula page for worked examples.
Use the millimeters to inch converter. The reverse formula is: mm ÷ 25.4 = in.
The calculator uses the full-precision conversion factor for accuracy. Table values and displayed results are rounded for readability.
The conversion formula (in × 25.4 = mm) is based on internationally defined standards. Displayed results are rounded for readability, while the calculator uses the full-precision factor.
person Written by Sean Day verified Reviewed by UnitCompare update Last updated Mar 28, 2026