What is the Triangle Area Calculator?
The triangle area calculator works out the area from a base and height, or from all three side lengths using Heron formula when the height is unknown.
How to use the Triangle Area tool
- Enter Method, Base or side A and Height or side B.
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
Area = ½ × base × height. Heron: s = (a + b + c) ÷ 2, Area = √(s × (s − a) × (s − b) × (s − c)).
Worked example
With method Base and height, base or side a 10, height or side b 6, the area comes to 30.
Frequently asked questions
Which method should I choose?
Use base and height when you know the height. Use the three-sides method when you only know the side lengths.
Why do I get an error with three sides?
The sum of any two sides must be greater than the third, or no triangle exists.
Related calculators
Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators.