单位转换
即时、私密且免费
分数英寸转毫米换算器.
将分数英寸转换为毫米，反之亦然。输入3 1/4、3-1/4、1/4或3.25即可得到精确的、已约简的分数。
输入数值
输入时结果会更新。
使用方法
1英寸精确定义为25.4毫米，因此这里的每次换算在您所选的舍入精度内都是精确的。
支持的输入格式：“3 1/4”、“3-1/4”、“1/4”、假分数如“5/4”，以及普通小数如“3.25”。
结果始终为最简形式——您得到的是1/2而非8/16，四舍五入为整英寸的数值会显示为1，而非16/16。
框架施工和普通木工建议选择1/16，橱柜及细木工建议选择1/32，机械加工或精细木工建议选择1/64。
常见问题
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.