This tool converts length from inches (in) to millimeters (mm) using the internationally adopted definition of the inch and SI decimal prefixes. It is suitable for technical drawings, hardware specs, and manufacturing where inch-based parts must be expressed in SI.

Inches (in) to Millimeters (mm) Converter

Enter a value in the field below and press the button

Inches (in)

Result in Millimeters (mm)

mm to in
Calculation process will appear here.
Decimal Places
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How to use

  1. Enter a value in inches in the input field.
  2. Set desired decimal places for the result.
  3. Select Convert to display millimeters and the calculation line.
  4. Use Copy Result to place the value on your clipboard.
  5. Use Clear All to reset inputs and outputs.
  6. The Swap control links to the reverse calculator (millimeters to inches).

Definitions and unit facts

Inch (in) — A unit of length in the U.S. customary and Imperial systems. Since 1959, it is defined exactly by the metric system: 1 in = 25.4 mm. Common abbreviations: in, ″. System: U.S. customary/Imperial. In SI terms: 1 in = 0.0254 m exactly; in millimeters: 25.4 mm exactly.

Millimeter (mm) — An SI unit of length equal to one thousandth of a meter: 1 mm = 0.001 m. Common abbreviation: mm. System: SI. In U.S. customary terms: 1 mm = 0.03937007874 in (derived from 1 in = 25.4 mm).

Conversion formula

millimeters = inches × 25.4. Source: NIST — SI Units: Length.

Inch to millimeter ratio on the measuring tool

Here you can see the ratio of inch to millimeter on the measuring tool.

Conversion table

Inches (in)Millimeters (mm)
0.1253.17
0.256.35
0.5012.70
0.7519.05
1.0025.40
1.5038.10
2.0050.80
3.0076.20
4.00101.60
5.00127.00
6.00152.40
8.00203.20
10.00254.00
12.00304.80
14.00355.60
16.00406.40
18.00457.20
20.00508.00
24.00609.60
36.00914.40

Real-world examples

  • U.S. penny diameter: 0.75 in = 19.05 mm
  • U.S. quarter diameter: 0.955 in = 24.26 mm
  • Credit card width (ID-1): 3.370 in = 85.60 mm
  • Credit card height (ID-1): 2.125 in = 53.98 mm
  • Rack unit height (1U): 1.75 in = 44.45 mm
  • Standard 19-inch rack width: 19.00 in = 482.60 mm
  • Optical disc diameter (CD/DVD): 4.724 in = 120.00 mm
  • U.S. Letter width: 8.50 in = 215.90 mm
  • U.S. Letter height: 11.00 in = 279.40 mm
  • 3.5-inch floppy disk diameter: 3.50 in = 88.90 mm

What do you use this calculator for? If you need another online tool, request it in the comments.