Equilateral Triangle Calculator
Area, height, perimeter and radii from one side.
Enter your values
ⓘ Live results
Results
- Area
- 43.30127 sq units
- Height
- 8.66025
- Perimeter
- 30
- Inradius
- 2.88675
- Circumradius
- 5.7735
- Each angle
- 60°
- Semiperimeter
- 15
Quick answer
An equilateral triangle with side s has area (√3 ÷ 4)s² and height (√3 ÷ 2)s, with all three angles at 60°.
A = (√3 ÷ 4)s²
How to use the Equilateral Triangle Calculator
- 1Enter the side length in any unit.
- 2Read the area, height and both radii.
- 3Use the inradius when you need to fit a circle inside the triangle.
Worked example
Using the values the calculator loads with:
Inputs
- Side length10 units
Results
- Area43.30127 sq units
- Height8.66025
- Perimeter30
- Inradius2.88675
- Circumradius5.7735
- Each angle60°
- Semiperimeter15
Frequently asked questions
Why is the height s√3 ÷ 2?
Split the triangle down the middle and you get a 30-60-90 right triangle, whose long leg is √3 ÷ 2 times the hypotenuse.
Is an equilateral triangle also equiangular?
Yes — equal sides force equal angles, all 60°, and the converse holds too.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.