millimeter

American  

[mil-uh-mee-ter] / ˈmɪl əˌmi tər /

especially British, millimetre

noun

• millimeters
  plural

1. a unit of length equal to one thousandth of a meter and equivalent to 0.03937 inch. mm

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millimeter Scientific  

/ mĭl′ə-mē′tər /

1. A unit of length in the metric system equal to 0.001 meter.

2. See Table at measurement

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Other Word Forms

Derived Forms

• millimetric
  adjective

Inflected Forms

Nouns

• millimeters
  plural

Etymology

Origin of millimeter

First recorded in 1800–10; from French millimètre; see milli-, meter ¹

Explanation

A millimeter is a tiny unit of measurement. The thickness of a dime is a little more than a millimeter, and there are a thousand millimeters in a meter. If you're using metric units to measure the length of something, you'll be dealing in meters and variations on meters, including millimeters. Look at a ruler that includes centimeters, the units of metric measurement that are closest in length to inches. The smallest units marked on the ruler are millimeters — there are ten of them in each centimeter. Although the word millimeter sounds like "million," it actually means "thousandth of a meter."

Example Sentences

See Examples For:

millimeter millimeters

Those optical frequencies can then be converted into multiple high-frequency electromagnetic signals known as millimeter waves.

From Science Daily ● Aug. 24, 2026

Earlier research demonstrated that microcombs could produce a single precise millimeter wave frequency.

From Science Daily ● Aug. 24, 2026

Granulation dates to Mesopotamia, but the Etruscans elevated the practice, using granules as small as 0.14 millimeter in diameter, one-seventh the size of those used by Mesopotamians and Egyptians.

From The Wall Street Journal ● Jul. 18, 2026

As part of the restructure, ownership of a facility making 200 millimeter chips, in which Tower currently holds a majority stake, will transfer to Nuvoton Technology.

From The Wall Street Journal ● Jul. 14, 2026

Goosebumps rise up on every millimeter of my body.

From "Love, Hate & Other Filters" by Samira Ahmed

Although the physical ring may measure only a few millimeters, the total effective distance traveled by the light depends on how little energy is lost from the waveguide each time it goes around.

From Science Daily ● Aug. 17, 2026

Sea-level rise is measured in millimeters, so tiny drifts in the reference frame prevent accurate calculations of coastal risk.

From The Wall Street Journal ● Aug. 7, 2026

The region, made up of mountains surrounded by a desert steppe, receives just over 100 millimeters of annual rainfall, classifying it as an desert.

From Barron's ● Jun. 15, 2026

A traditional arthroscope measures about 4 millimeters in diameter.

From The Wall Street Journal ● May 26, 2026

She painted on over forty coats—she lost count—but by the time her lacquer had run out, the surface was at least five millimeters thick.

From "The Amber Spyglass" by Philip Pullman