diameter

American  

[dahy-am-i-ter] / daɪˈæm ɪ tər /

noun

• diameters
  plural

1. Geometry.

   1. a straight line passing through the center of a circle or sphere and meeting the circumference or surface at each end.

   2. a straight line passing from side to side of any figure or body, through its center.

2. the length of such a line.

3. the width of a circular or cylindrical object.

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diameter British  

/ daɪˈæmɪtə /

noun

1. 1. a straight line connecting the centre of a geometric figure, esp a circle or sphere, with two points on the perimeter or surface

   2. the length of such a line

2. the thickness of something, esp with circular cross section

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diameter Scientific  

/ dī-ăm′ĭ-tər /

1. A straight line segment that passes through the center of a circle or sphere from one side to the other.

2. The length of such a line segment.

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diameter Cultural  

1. A straight line passing through the center of a figure, especially a circle or sphere, and joining two opposite points on its circumference.

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Other Word Forms

Noun Inflected Forms

• diameters
  plural

Etymology

Origin of diameter

First recorded in 1350–1400; Middle English diametre, from Old French, from Latin diametros, from Greek diámetros “diagonal, diameter,” from dia- dia- + -metros, derivative of métron meter ¹

Explanation

It's good to know where the diameter of a circular object is if you have to split a cookie between two 5-year-old kids. Think of a round chocolate chip cookie. The diameter of the cookie is a line that divides the cookie into two equal halves, through the center of the cookie. The diameter of a circle or sphere is a line that passes through the center and starts and ends and two opposite points on its perimeter or edge. The diameter is also the length of that line. In math class, teachers often ask you to use the diameter of a circle to find its area. This is a good skill to have if you are trying to figure out whether the 14 inch or 16 inch pizza is a better deal.

Example Sentences

See Examples For:

diameter diameters

First created in 1980 in the Mojave Desert, the work involved students spreading red, yellow and black pigment in a geometric pattern more than 600 feet in diameter.

From Los Angeles Times ● Oct. 13, 2026

Upon arrival, the Fire Department located five separate spot fires, all about five feet in diameter.

From Los Angeles Times ● Sep. 12, 2026

At its peak, roughly 93% of the Moon's diameter will be covered, making the event look close to a total eclipse.

From BBC ● Aug. 27, 2026

At the eclipse's maximum point, about 93% of the Moon's diameter will lie within Earth's dark central shadow, known as the umbra.

From Science Daily ● Aug. 5, 2026

Halfway to the ceiling, seemingly in midair, were five gigantic electric chandeliers, the largest ever built, each seventy-five feet in diameter and generating 828,000 candlepower.

From "The Devil in the White City" by Erik Larson

Which is to say, Porsche invented an entirely new flat-six—different bore diameters and everything—just to clear 11 centimeters under the engine cover.

From The Wall Street Journal ● Oct. 30, 2025

Astronomers these days are really interested in sub-Neptune planets, meaning those with diameters larger than Earth but smaller than Neptune.

From Salon ● May 31, 2025

Hailstones, some with diameters of around 2 inches, also fell over parts of the city.

From New York Times ● Apr. 27, 2024

PM 2.5 refers to the level of tiny, hazardous particles - with diameters that are 2.5 micrometres or smaller - that can enter bloodstreams though the lungs.

From BBC ● Mar. 6, 2024

In a train of epicycloidal gearing in which the pinion or smallest wheel has radial flanks, the flanks of the teeth will become spread as the diameters of the wheels in the train increase.

From Modern Machine-Shop Practice, Volumes I and II by Joshua Rose

Related Words

• width