Equilateral Triangle Calculator

An equilateral triangle has three equal sides and three 60° angles. Everything about it follows from one side length.

Results update as you type.

Area

15.58845727

(√3 ÷ 4) × side²

Perimeter
18
Height
5.196152423
Inradius
1.732050808
Circumradius
3.464101615

About this calculator

Enter the side.

How to use it

  1. Enter the side length.
  2. Read the measurements.

The formula

Area = (√3 ÷ 4) × a²; height = (√3 ÷ 2) × a
a
side length

Worked example

Side 6

  1. Area = √3 ÷ 4 × 36 ≈ 15.59.
  2. Height ≈ 5.196; circumradius ≈ 3.464.

What the result means

The circumradius is twice the inradius.

Assumptions

  • All lengths in the same unit.

Limitations

  • Results are rounded to 10 significant figures.

Frequently asked questions

What is the area of an equilateral triangle?

(√3/4) × side².

What is its height?

(√3/2) × side.

What are its angles?

All 60°.

Last reviewed on 3 October 2026. Found a mistake? Tell us.