Maths & numbers
Triangle calculator
Find area and perimeter from three side lengths.
A clear answer. Here’s how.
Uses a rearranged form of Heron’s formula. All sides must be positive and satisfy the triangle inequality. Use the same length unit for every side.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Side a
- 3
- Side b
- 4
- Side c
- 5
Example result
- Area (square units)
- 6
- Perimeter
- 12