Micrometer | Definition, Conversion, & Facts | Britannica

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micrometre unit of measurement Ask Anything Homework Help Also known as: μm, micron Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Jan. 28, 2026 •History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

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micrometre, metric unit of measure for length equal to 0.001 mm, or about 0.000039 inch. Its symbol is μm. The micrometre is commonly employed to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles. Minute distances—for example, the wavelengths of infrared radiation—are also given in micrometres.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Erik Gregersen.