How this calculator works
The international inch is defined as exactly 25.4 mm. Divide the metric dimension by 25.4 to obtain decimal inches, or multiply inches by 25.4 to reverse it. The common-size table includes half-inch and whole-inch equivalents without imposing a preferred manufactured size.
Formula
inches = mm / 25.4; mm = inches x 25.4.
Worked example
A 127 mm component is exactly 5 inches long. A 0.375 inch dimension is exactly 9.525 mm.
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Frequently asked questions
Is 25.4 an exact conversion factor?
Yes. The international inch is exactly 25.4 mm.
How do I convert a fractional inch?
Enter its decimal value in reverse mode, such as 0.375 for 3/8 inch.
Does this add machining tolerance?
No. It changes units for the entered nominal dimension; tolerances must be converted separately.