Area of an equilateral triangle - Math Open Reference

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Area of an equilateral triangle

The area of an equilateral triangle (all sides congruent) can be found using the formula

where s is the length of one side of the triangle.

Try this Drag the orange dots on each vertex to reshape the triangle. The formula shown will recalculate the area using this method.

When you know all three sides of a triangle, the usual way to find the area is to use Heron's Formula. But in the case of equilateral triangles, where all three sides are the same length, there is a simpler formula:

Calculator

where
s is the length of any side of the triangle.

Methods for finding triangle area

If you know:	Use this
Base and altitude	"Half base times height" method
All 3 sides	Heron's Formula
Two sides and included angle	Side-angle-side method
x,y coordinates of the vertices	Area of a triangle- by formula (Coordinate Geometry) Area of a triangle - box method (Coordinate Geometry)
The triangle is equilateral	Area of an equilateral triangle

Things to try

In the figure above, click on "hide details"
Drag the vertices of the triangle to make a new size triangle
Calculate the are using this method
Click "show details" to verify your answer

Methods for finding triangle area

Things to try

Related triangle topics

General

Perimeter / Area

Triangle types

Triangle centers

Congruence and Similarity

Solving triangles

Triangle quizzes and exercises