pe·​rim·​e·​ter | \ pə-ˈri-mə-tər How to pronounce perimeter (audio) \

Definition of perimeter

1a : the boundary of a closed plane figure
b : the length of a perimeter
2 : a line or strip bounding or protecting an area
3 : outer limits often used in plural
4 : the part of a basketball court outside the three-point line

Parameter vs. Perimeter

It's very easy to confuse parameter with perimeter. Not only do the two words sound the same, they both connote a boundary or limit.

When parameter is used to mean "a boundary or limit," it is usually in its plural form, and often as the object of a preposition such as within or beyond:

Let's face it, managing weight loss or maintenance can be trying enough within the parameters of a daily routine.
Geoff Kerr, Weight Watchers, November 1991

Though candor sometimes encourages Bruno to "stray beyond the parameters of good taste," his interaction with Lydia is always convincingly portrayed as a loving, tender relationship.
Ron Charles, The Washington Post, 8 Feb. 2011

In geometry, perimeter refers to the boundary of a closed plane figure. You might remember calculating perimeters in school. If each side of an equilateral triangle measures 9 feet, then the perimeter of the triangle measures 27 feet. In more general use, perimeter describes an outer stretch, as in "The college president lived in a house on the perimeter of the campus."

Parameter originally had a meaning pertaining to mathematics as well. The dictionary defines it as "an arbitrary constant whose value characterizes a member of a system (as a family of curves); also : a quantity (as a mean or variance) that describes a statistical population" as well as "an independent variable used to express the coordinates of a variable point and functions of them."

Some twentieth-century usage commentators objected to the use of a scientific-sounding word like parameter in general contexts (as in the examples above), especially to mean "a limit or boundary," theorizing that perimeter must have been what the speaker or writer intended.

However, perimeter was not often used in the phrasings that parameter is used in (that is, as the object of within or beyond) until much later. In fact, a word such as bounds or range or confines often serves as a more appropriate equivalent for parameter than the marginal connotations of perimeter:

But a true novel is an extended piece of fiction: Length is clearly one of its parameters.
Anthony Burgess, The New York Times Book Review, 5 Feb. 1984

Shields will then subsume that request in the overall City operating budget that he will recommend to the City Council in mid-March, and the Council will make its final decisions on the parameters of the budget, including any tax increases or cuts, by the end of April.
Nicholas F. Benton, The Falls Church News Press, 6 Jan. 2016

Did you know?

The perimeter of a prison is ringed with high walls and watchtowers, and the entire perimeter of Australia is bounded by water. In geometry, you may be asked to calculate the perimeter of various geometrical shapes. In basketball, the perimeter is the area beyond the free-throw circle; a "perimeter player" tends to stay outside that circle. Try not to confuse this word with parameter, which usually means a rule or limit that controls what something is or how it can be done.

Examples of perimeter in a Sentence

He scored from the perimeter. soldiers guarding the perimeter of the camp
Recent Examples on the Web The ball seemed stuck on the perimeter and Xavier went 0-for-14 from 3 in the second half. Adam Baum, The Enquirer, 23 Dec. 2021 Indiana's best three-level scorer, freshman guard Tamar Bates, was out, attending a family funeral in the Kansas City area, and so the Hoosiers were without a significant perimeter-scoring weapon. Dustin Dopirak, The Indianapolis Star, 19 Dec. 2021 The palisade played an important function, providing a protective barrier by the Alamo Church, where there was no stone mission-era wall, like those that surrounded most of the compound’s perimeter. Scott Huddleston, San Antonio Express-News, 16 Dec. 2021 Matt Bradley making quicker decisions and getting downhill sooner instead of pounding the ball on the perimeter assessing options. Mark Zeigler, San Diego Union-Tribune, 16 Dec. 2021 Their giant open walls don’t rely on vertical supports on the building’s perimeter to resist wind load, said Frank Lombardo, an assistant professor at University of Illinois at Urbana-Champaign who researches wind engineering and hazard mitigation. Washington Post, 15 Dec. 2021 Tons of speed, perimeter playmakers on offense and defense, and explosive quarterback talent. Jeremy Cluff, The Arizona Republic, 30 Nov. 2021 Place 5 slices of soppressata around the perimeter of the sauce and one in the center. Carlo Mirarchi, Robb Report, 30 Nov. 2021 Ibaka, a 35% career three-point shooter, typically was stationed beyond the three-point line for spacing, allowing Hartenstein to run between the paint and perimeter setting screens and rolling to the rim. Andrew Greif, Los Angeles Times, 26 Nov. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'perimeter.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of perimeter

15th century, in the meaning defined at sense 1a

History and Etymology for perimeter

Middle English perimetre, from Latin perimetros, from Greek, from peri- + metron measure — more at measure

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The first known use of perimeter was in the 15th century

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Last Updated

8 Jan 2022

Cite this Entry

“Perimeter.” Dictionary, Merriam-Webster, Accessed 16 Jan. 2022.

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More Definitions for perimeter



English Language Learners Definition of perimeter

: the outside edge of an area or surface
: the total length of the lines that form a shape
: the area on a basketball court that is not close to the basket


pe·​rim·​e·​ter | \ pə-ˈri-mə-tər How to pronounce perimeter (audio) \

Kids Definition of perimeter

1 : the whole outer boundary of a figure or area
2 : the length of the boundary of a figure


pe·​rim·​e·​ter | \ pə-ˈrim-ət-ər How to pronounce perimeter (audio) \

Medical Definition of perimeter

1a : the boundary of a closed plane figure
b : the length of a perimeter
2 : an instrument for examining the discriminative powers of different parts of the retina often consisting of an adjustable semicircular arm with a fixation point for the eye and variable stations for the visual stimuli

More from Merriam-Webster on perimeter

Nglish: Translation of perimeter for Spanish Speakers

Britannica English: Translation of perimeter for Arabic Speakers


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