Convert tiny-scale lengths between µm, mm, cm, mil, and in, with high-precision output for craft, manufacturing, and science use.
Precision length
Switch between micrometres, millimetres, centimetres, thou, and inches for machining, print tolerances, coatings, and other close-range measurements.
Result
Also in Length & Distance
Precision Measurement
A small measurements converter helps when the same tolerance or material thickness is described in different unit families. Machine shops, print suppliers, coatings data sheets, and technical drawings often mix micrometres, millimetres, thou, and inches, so a precise converter saves repeated mental arithmetic.
At close tolerances, a tiny change in the number can be a meaningful change in the part or finish. A coating thickness, shim, film, paper stock, or machining clearance may be written in micrometres on one document and in thou or inches on another.
That is why a precision converter needs to keep the metric and customary families visible at the same time. The underlying length has not changed. Only the way it is being expressed has.
Metric small-length units are straightforward SI-prefix steps. One millimetre equals one thousand micrometres, and one centimetre equals ten millimetres. The imperial side is anchored by the exact inch definition, then thou is derived from it as one thousandth of an inch.
Because the inch is defined exactly in metric terms, the customary units can be translated cleanly into the SI family without approximation drift in the core factor itself.
1 mm = 1,000 µm
Metric prefix relationship between millimetres and micrometres.
1 in = 25.4 mm (exact)
Exact international inch definition used for all downstream customary conversions.
1 thou = 0.001 in = 25.4 µm
Connects the common workshop thou or mil unit back to both inch and SI notation.
Micrometres and millimetres are common in coatings, manufactured parts, lab work, and metric-first engineering documentation. Centimetres are less common for very fine tolerances, but they still appear in packaging, product dimensions, and mixed-format supplier information.
Thou and inches remain common in US workshop language, print stock descriptions, and legacy machining or fabrication references. When a specification uses thou, it is best treated as a customary industry unit rather than as an SI standard.
Frequently asked questions
In workshop and fabrication usage, yes. Both usually mean one thousandth of an inch, or 0.001 in. That equals 25.4 micrometres.
There are exactly 1,000 micrometres in 1 millimetre. The relationship comes directly from SI prefixes: milli means one-thousandth of a metre, and micro means one-millionth of a metre.
Because many real specs still bridge metric and inch-based shop language. Including inches makes it easier to move between formal SI notation and customary tolerances or material sheets.
No. It converts units accurately, but it does not decide what tolerance is acceptable for a part, finish, or process. That still depends on the engineering or production requirement.
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