All three sides and angles of an equilateral triangle are equal, so one measurement defines everything.
How to use the Equilateral Triangle Calculator
- Side length
- Want to work backwards? Type a value into Area and Side length is calculated for you.
Results update as you type, and every field accepts the units shown in its menu.
How it works
The height comes from splitting the triangle into two 30-60-90 triangles.
What each result means
- Area = sqrt(3)÷4 × [Side length]^2
- Height = sqrt(3)÷2 × [Side length]
- Perimeter = 3×[Side length]
- Inradius = [Side length] ÷ (2×sqrt(3))
- Circumradius = [Side length] ÷ sqrt(3)
Example values
How the main result changes when Side length changes and everything else stays at the example values above:
| Side length (m) | Area (m²) |
|---|---|
| 5 | 10.83 |
| 7.5 | 24.36 |
| 10 | 43.3 |
| 12.5 | 67.66 |
| 15 | 97.43 |
| 20 | 173.21 |
Formula
h = √3 ÷ 2 × aArea = √3 ÷ 4 × a²Worked example
Inputs — Side length: 10 m.
Results — Area = 43.3 m²; Height = 8.66 m; Perimeter = 30 m; Inradius = 2.89 m; Circumradius = 5.77 m.
Frequently asked questions
What are the angles?
Each is 60°.
How is it related to a hexagon?
A regular hexagon is made of six equilateral triangles.
What formula does the Equilateral Triangle Calculator use?
h = √3 ÷ 2 × a.
Can I work backwards from the result?
Yes. Type the result you want into Area and the calculator finds the matching side length.