Image: Wikimedia Commons

equilateral triangle

Geometric shape with three sides of equal length

EntityQ157002

Also known as regular triangle · equiangular triangle

Subclass of: regular convex polygon
, simplex
, constructible polygon
+3 more

Overview

From Wikipedia, the free encyclopedia · Read full article · Text CC BY-SA 4.0

An equilateral triangle is a triangle with three sides of equal length and three equal angles. It is a regular polygon, occasionally known as the regular triangle. It is a special case of an isosceles triangle by modern definition. Its internal angle is 60 degrees or π/3 radians. Its perimeter is three times the side length. Its area is a quarter of the square root of three multiplied with its squared side length. Its appearance is unchanged by three reflection lines, each of which passing through a vertex to the midpoint of the opposite edge, and three rotations around its centroid ; this property is related to the dihedral group of order 6 in algebra.

Overview

All data

36 statements · 11% with external sources · numbers in brackets are citations

Has facet polytope: edge quantity: 3
Schläfli symbol: {3}
Has characteristic: perimeter defining formula: P=3a
plane area defining formula: A=\frac{\sqrt{3}}{4} a^2
inradius defining formula: r=\frac{\sqrt{3}}{6}a
circumradius defining formula: R=\frac{\sqrt{3}}{3}a
reflection symmetry
isoperimetric ratio numeric value: 12
Different from: triangle
scalene triangle
isosceles triangle
Opposite of: non-equilateral triangle

On other databases

17 identifiers linking equilateral triangle across the web's reference databases

Data quality

statements

11%

externally sourced

Source last edited November 2, 2026. AIDb refreshes this page daily.

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AIDb. (2026). equilateral triangle (Q157002). Retrieved from https://aidb.si/e/equilateral-triangle-Q157002