Triangle Area Calculator
Area from base and height, or all three sides.
Enter your values
ⓘ Live results
Results
- Area
- 26.832816
- Perimeter
- 24
- Semi-perimeter
- 12
- Height on side a
- 7.666519
Working
- 1s = 12
- 2A = √(12 × 5 × 4 × 3) = 26.8328
Quick answer
Triangle area is ½ × base × height, or Heron's formula √(s(s−a)(s−b)(s−c)) when you only know the three sides.
A = ½bh or √(s(s−a)(s−b)(s−c))
How to use the Triangle Area Calculator
- 1Choose whether you know base and height or all three sides.
- 2Enter the measurements.
- 3Read the area and perimeter.
Worked example
Using the values the calculator loads with:
Inputs
- MethodThree sides (Heron)
- Base or side a7
- Height or side b8
- Side c9
Results
- Area26.832816
- Perimeter24
- Semi-perimeter12
- Height on side a7.666519
- s = 12
- A = √(12 × 5 × 4 × 3) = 26.8328
Frequently asked questions
What is Heron's formula?
A way to get the area from side lengths alone, using the semi-perimeter s = (a+b+c)/2.
Why does my triangle fail?
Any two sides must sum to more than the third — otherwise the shape cannot close.
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.