Inches to Millimetres

How to use this calculator

1. Enter length in in.
2. Select Calculate and keep the output unit with the answer.

Before you use the answer

Keep a measurement sheet separate from the purchasing allowance. Record which dimensions are internal, which openings were subtracted and which items must be bought as full packs. These are material and schedule estimates; they do not establish structural adequacy or building-code compliance.

Enter mixed fractions as decimals; two and one-half inches is 2.5.

Does it save my inputs?

No calculation history is stored by this website. The calculator works locally in your browser. See the privacy policy for hosting and contact details.

Why might a result be approximate?

Measurement uncertainty, ideal-model assumptions and floating-point rounding can all matter. Displaying more digits does not improve the original measurement.