About the equilateral triangle calculator
All three sides of an equilateral triangle are equal and every angle is 60°, so one measurement determines the whole shape. The height splits it into two 30-60-90 triangles, which is where the √3 in every formula comes from.
Formulas
| Height | h = (√3/2)a |
| Area | K = (√3/4)a² |
| Perimeter | P = 3a |
| Inradius / circumradius | r = a/(2√3), R = a/√3 = 2r |
Frequently asked questions
What is the area of an equilateral triangle?
K = (√3/4)·a². A triangle with side 6 has area 9√3 ≈ 15.588.
What is the height of an equilateral triangle?
h = (√3/2)·a ≈ 0.866·a.