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

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

The findings may also prove useful in medicine, particularly in microfluidic systems where fluids move through channels smaller than a millimeter.

From Science Daily ● Jun. 3, 2026

While a single 300 millimeter silicon wafer normally produces a few dozen chips, Cerebras uses the entire wafer for one chip, about the size of a dinner plate.

From Barron's ● May 15, 2026

The chip is giant, taking up an entire 300 millimeter silicon wafer, almost a foot long across the chip’s diagonal line.

From Barron's ● May 11, 2026

Inside was fitted an old 37 millimeter bronze flarepistol.

From "The Road" by Cormac McCarthy

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 simulations suggest that a detector of this size could achieve spatial resolution of a few millimeters, placing it on par with state-of-the-art plastic scintillator detectors.

From Science Daily ● Jul. 17, 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

The new PCs will be as slim as 14 millimeters thick, and the lightest will weigh less than 3 pounds.

From The Wall Street Journal ● Jun. 1, 2026

Then I went back behind him and turned the dials extremely slowly, a few millimeters at a time.

From "Extremely Loud and Incredibly Close" by Jonathan Safran Foer