One inch
Input: 1 in
Output: 25.4 mm
1 × 25.4 = 25.4 millimeters.
inches to mm converter
Use this to turn inch dimensions into millimeters for tooling, CAD, and hardware.
Millimeters:
Formula and algorithm
- millimeters = inches × 25.4
- Constant used: 1 inch = 25.4 millimeters (exact).
- Multiply the inch value by 25.4 to get millimeters.
Worked examples
Pipe length
Input: 7 in
Output: 177.8 mm
7 × 25.4 = 177.8 millimeters.
Half inch
Input: 0.5 in
Output: 12.7 mm
0.5 × 25.4 = 12.7 millimeters.
FAQ
What is 1 inch in mm?
Exactly 25.4 millimeters.
How do I convert fractional inches?
Convert the fraction to a decimal first (e.g. 1/4 = 0.25) then multiply by 25.4.
Does scientific notation work?
Yes, browser number inputs accept values like 1e2 for 100 inches.
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Updated: June 7, 2026