Equilateral Triangle Calculator
Area, height, perimeter and radii from one side.
Enter your values
Enter the side length in units.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Area, height, perimeter and radii from one side. |
|---|---|
| Category | Math |
| Inputs needed | Side length |
| Main output | Area |
| Formula | A = (√3 ÷ 4)s² |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Side length(units)
- Enter the side length in units.
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.
What do I need to enter into the Equilateral Triangle Calculator?
Just 1 value: side length. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Equilateral Triangle Calculator work out the answer?
An equilateral triangle with side s has area (√3 ÷ 4)s² and height (√3 ÷ 2)s, with all three angles at 60°. It applies the formula A = (√3 ÷ 4)s² and shows the working so you can check each step by hand.
Is the Equilateral Triangle Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.