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

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

"The millimeter and submillimeter radio bands remain almost completely unexplored for SETI, so this is really about opening up a new area of parameter space to search."

From Science Daily ● Jul. 30, 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

Only Jonah was in a position to see that she didn’t actually touch it, that she kept a millimeter of air between her fingertips and the rock.

From "Found" by Margaret Peterson Haddix

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

From Science Daily ● Sep. 4, 2026

“Combine 2 millimeters of rain with 35 degrees Centigrade—it’s bonkers,” O’Malley said.

From The Wall Street Journal ● Aug. 31, 2026

In July, just 2 millimeters of rain fell in East Anglia, drying out fields and shriveling vegetables in one of the U.K.’s breadbaskets.

From The Wall Street Journal ● Aug. 31, 2026

The United States, the Netherlands, and Italy also have elevated rates, averaging approximately 4 to 5 millimeters per year.

From Science Daily ● Aug. 3, 2026

His birthday at Alton Towers was canceled, Gavin Coley’s eyes sunk into his skull a few millimeters, and a year later his parents got divorced.

From "Black Swan Green" by David Mitchell