Inches to MM Converter

Convert inches to millimeters instantly with our free online inches to mm converter. Enter any length in inches and see the exact equivalent in millimeters immediately.

FROM1inInches=TO25.4mmMillimeters
inches to mm showing 1 in equals 25.4 mm
in
mm
Quick Values

How to Use This Inch to Millimeter Converter

  1. 1Enter the length in inches (in) in the input field above.
  2. 2The converter automatically calculates the exact length in millimeters (mm).
  3. 3Use the swap button to switch between inches to mm and mm to inches conversion.
  4. 4Check the common conversions table for fractional inch measurements.

Inch to Millimeter Formula

To convert inches to millimeters, multiply the length in inches by 25.4. The formula is: millimeters = inches × 25.4. This exact conversion factor was established in 1959, defining the inch as precisely 25.4 millimeters.

For example, to convert 2 inches to mm: 2 × 25.4 = 50.8 mm. To convert 0.5 inches to mm: 0.5 × 25.4 = 12.7 mm.

Relative Size Comparison1 in25.40 mminmm00.25x0.5x0.75x1
Scale diagram showing the relative size of in compared to mm for inches to mm

Common Inches to Millimeters Conversions

Inch (in)Millimeter (mm)
0.1253.17
0.256.35
0.512.7
0.7519.05
125.4
1.538.1
250.8
376.2
4101.6
5127
6152.4
8203.2
10254
12304.8
16406.4
20508
24609.6
36914.4
481,219.2
601,524

About Inches and Millimeters

The inch is a unit of length equal to exactly 25.4 millimeters. It remains the standard unit of measurement in the United States for construction materials, screen sizes, and countless everyday items. Millimeters are used in the metric system for precision engineering, 3D printing, and scientific applications. Converting inches to millimeters is necessary when working with metric specifications, ordering components from international suppliers, setting up 3D printer settings, or collaborating on projects that use mixed measurement systems. Our converter handles both whole numbers and fractional inch values with precision.

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Frequently Asked Questions About Inch to Millimeter

1 inch equals exactly 25.4 millimeters. This has been the internationally standardized value since 1959.
The formula is: millimeters = inches × 25.4. Simply multiply any inch measurement by 25.4 to get the exact millimeter equivalent.
1/2 inch equals exactly 12.7 mm. This is because 0.5 × 25.4 = 12.7.
3/4 inch equals exactly 19.05 mm. This is because 0.75 × 25.4 = 19.05.
Multiply the inch size by 25.4. For example, a 1/2 inch wrench is 12.7 mm, and a 9/16 inch wrench is approximately 14.29 mm.
No, 25 mm is slightly less than 1 inch. Exactly 25.4 mm equals 1 inch, so 25 mm is approximately 0.984 inches.