Convert millimetres to inches

Formula: in = mm × 0.03937

mm to in quick reference table

Everyday mm values, converted

• 10 mm = 0.393701 in — one centimetre.
• 25 mm = 0.984252 in — roughly an inch of rainfall or timber.

Where mm to in comes up

Length conversions come up in DIY and construction, screen and print sizing, running distances, and clothing or furniture measurements ordered from abroad. Mixed-unit plans are the usual reason a cut ends up wrong.

Doing mm to in in your head

Divide by 25.4 for a close estimate; the calculator above uses the full factor of 0.03937.

Precision and rounding

One millimetre is exactly 0.03937 inches under the current definitions of both units, so the only judgement call is how many digits you keep. Two decimal places is already finer than most household scales and tape measures can read, while engineering and medical work usually keeps the full factor and rounds once at the end rather than at every step.