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.

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:

(C) 2009 Copyright Math Open Reference. All rights reserved