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

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Etymology

Origin of millimeter

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

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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

The finished fiber measures less than half a millimeter across.

From Science Daily ● Sep. 21, 2026

They grow about a centimeter or two a year and by sampling cores at the millimeter scale, the team was able to develop windows of monthly temperature records scattered across the past millennium.

From Barron's ● Aug. 27, 2026

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

From Science Daily ● Aug. 24, 2026

"That has paid off really well for us because there are a lot of people out there that are seeking that 70 millimeter presentation."

From Barron's ● Jul. 26, 2026

For the first time I feel the weight of every single inch, every millimeter, of the six feet between us.

From "Five Feet Apart" by Rachael Lippincott

It measured an impressive 86.6 millimeters, or approximately 3.4 inches, excluding its tail, claws, and antennae.

From Science Daily ● Oct. 16, 2026

They also had to be in direct contact -- a few millimeters apart, and nothing significant happened.

From Barron's ● Oct. 14, 2026

A reading of 120 over 80, measured in millimeters of mercury, could indicate prehypertension.

From The Wall Street Journal ● Oct. 11, 2026

Each colony was positioned about 5 millimeters from its nearest neighbor.

From Science Daily ● Sep. 4, 2026

A typical paramecium, for instance, is about two microns wide, 0.002 millimeters, which is really very small.

From "A Short History of Nearly Everything" by Bill Bryson

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