Convertisseur de Pouces Fractionnaires en MM.

How many millimetres are in an inch?

Exactly 25.4 mm. The international inch has been defined as precisely 25.4 millimetres since 1959, so inch-to-millimetre conversion is exact — the only approximation comes from rounding the fraction you read off a tape measure.

What input formats does this accept?

Mixed numbers with a space or hyphen ("3 1/4" or "3-1/4"), bare fractions ("1/4"), improper fractions ("5/4" = 1.25), and plain decimals ("3.25"). An inch mark or the word "in" on the end is fine too. Anything else returns a clear error rather than a silent wrong answer.

Why does it show 1/2 instead of 8/16?

Fractions are always reduced to lowest terms with a greatest-common-divisor step, so you get the form you would actually say out loud. For the same reason, a measurement that rounds up to a whole inch displays as "1", never "16/16".

Which precision should I choose — 1/16, 1/32 or 1/64?

1/16 in (1.59 mm) is the standard for framing, general carpentry and most tape measures. 1/32 in (0.79 mm) suits cabinetry, joinery and trim work. 1/64 in (0.40 mm) is for machining, metalwork and fine woodworking where a hair of slop matters.

How do I convert a decimal like 0.375 into a fraction?

Type it straight into the inches field. 0.375 in becomes 3/8 in (9.525 mm). The calculator rounds to your chosen denominator and then reduces, so decimals that land exactly on a fraction come out clean.