di·​am·​e·​ter dī-ˈa-mə-tər How to pronounce diameter (audio)
mathematics : a chord (see chord entry 3 sense 2) passing through the center of a figure or body
mathematics : the length of a straight line through the center of an object or space
the diameter of a circle
dug a hole nearly four feet in diameter
physics : a unit of enlargement used with a number to indicate magnification by a lens or optical system
an object one millimeter wide magnified 40 diameters appears 40 millimeters wide
diametral adjective

Examples of diameter in a Sentence

The dotted line indicates the diameter of the circle. What is the diameter of the tree trunk? Dig a hole that's two feet deep and three feet in diameter.
Recent Examples on the Web The West Hollywood structure would be a great deal smaller, at 49 feet in diameter. Karen Garcia, Los Angeles Times, 14 Nov. 2023 But the real genius feature is the interior waterproof pouch, which holds water bottles measuring up to 3.5 inches in diameter while simultaneously keeping them from becoming scratched. Jamie Allison Sanders, Peoplemag, 13 Nov. 2023 That means a tree with a trunk three inches in diameter would need three quarts per day. Katherine Owen, Southern Living, 12 Nov. 2023 One munition was a 75-mm projectile that was 3 inches in diameter and 11 inches long. Marlene Lenthang, NBC News, 10 Nov. 2023 Some of debris is quite small, while other parts are boulder-like in size, roughly 100 meters in diameter, says Erica Jawin, a geologist at the Smithsonian Air and Space Museum. Joshua Rapp Learn, Discover Magazine, 9 Nov. 2023 The new island was about 100 meters, or 328 feet, in diameter as of Oct. 30, according to a report by the Earthquake Research Institute at the University of Tokyo. Mike Ives, New York Times, 8 Nov. 2023 The small sample at the museum—the first available to the public—is about 0.3 inches in diameter and weighs just 0.005 ounces. Will Sullivan, Smithsonian Magazine, 7 Nov. 2023 What to Know About Napkin Rings Before Shopping Dimensions Most napkin rings have a hole around 2 inches in diameter, but this could vary based on design. Maya Polton, Better Homes & Gardens, 2 Nov. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'diameter.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Middle English diametre, from Middle French, from Latin diametros, from Greek, from dia- + metron measure — more at measure

First Known Use

14th century, in the meaning defined at sense 1

Time Traveler
The first known use of diameter was in the 14th century

Dictionary Entries Near diameter

Cite this Entry

“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 28 Nov. 2023.

Kids Definition


di·​am·​e·​ter dī-ˈam-ət-ər How to pronounce diameter (audio)
: a straight line passing through the center of a figure or body
especially : a line segment through the center of a circle with its ends on the circle's circumference
: the length of a diameter

Medical Definition


di·​am·​e·​ter dī-ˈam-ət-ər How to pronounce diameter (audio)
: a unit of magnification for an optical instrument equal to the number of times the linear dimensions of an object are apparently increased
a microscope magnifying 60 diameters
: one of the maximal breadths of a part of the body
the transverse diameter of the inlet of the pelvis
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