Millimeters to Micrometers (mm to µm)

1 millimeter equals 1,000 micrometers exactly.

1 millimeter = 1,000 micrometers

How to convert millimeters to micrometers

To convert millimeters to micrometers, multiply the number of millimeters by 1,000. This factor is exact. To go the other way, multiply micrometers by 0.001.

micrometers = millimeters × 1,000

Example: 10 millimeters = 10,000 micrometers.

About these units

Millimeter (mm)

Metric (SI)Current unit

One thousandth of a meter. Used in engineering, manufacturing and rainfall measurement.

Carl Friedrich Gauss put the millimeter at the base of his 1832 proposal for absolute units, pairing it with the milligram and the second, although the centimeter-based CGS system later won out among scientists. The name combines the metric prefix milli-, from the Latin for one thousand, with the meter. Since 1983 a millimeter has been tied to the speed of light: it is the distance light covers in 1/299,792,458,000 of a second.

Millimeters are the language of fine mechanical work. Standard rulers are divided into them, digital calipers commonly read to 0.01 mm, and mechanical pencil leads come in 0.5 and 0.7 mm. Copy paper is about 0.1 mm thick, and a thin hair, at 0.02 to 0.04 mm across, is close to the smallest thing the naked eye can see. A wave with a frequency of 300 GHz has a wavelength of 1 mm. An inch is exactly 25.4 mm. One trap for readers in the United States is that mil there traditionally means a thousandth of an inch, not a millimeter.

1 millimeter = 0.001 meters (exactly).

Sources: Wikipedia: Millimetre; Wikipedia: Centimetre-gram-second system of units; NIST Guide to the SI, Appendix B.8: conversion factors

Micrometer (µm)

Metric (SI)Current unit

One millionth of a meter, also called a micron. Typical bacteria are a few micrometers long; a human hair is roughly 70 µm thick.

Two names, micron and micrometer, have shared this unit for more than a century. The prefix micro- was adopted in 1873 alongside the CGS system, and in 1879 the term micron and the symbol μ were officially accepted for the micrometer when used on its own. That created a clash once SI came along: μ was also the symbol for the prefix micro-. The 13th CGPM revoked micron and its symbol in 1967 to 1968, leaving micrometer and μm as the official name and symbol, though micron lives on in everyday speech.

A micrometer is a thousandth of a millimeter, and it is the natural scale for biology and filtration. A typical red blood cell is 6 to 8 μm across, a bacterium is 1 to 10 μm long, and a fog droplet is around 10 μm. Human hair ranges from about 17 to 181 μm in diameter, and paper is 70 to 180 μm thick. Infrared radiation is measured in micrometers of wavelength, and wool is graded by fibre width. Some American writers keep micron because micrometer also names the caliper-style measuring tool.

1 micrometer = 0.000001 meters (exactly).

Sources: Wikipedia: Micrometre; Wikipedia: Metric prefix

Related conversions

See all length units.