Formula
Heron's formula uses the semi-perimeter s:
Area = √(s(s − a)(s − b)(s − c))
The perimeter page adds the sides instead of finding the area.
Assumptions
- The three lengths form a triangle.
- The area is the flat interior.
Worked example
Sides 3, 4, and 5 have area 6.
Input definitions
- Sides
- The three edge lengths. No angle is required.
Limitations
Results are rounded for display. This is a classroom calculation, not a measurement from a lab or a financial filing.
Questions
Do I need the height?
No. Three sides are enough for this formula.
Why is a 3-4-5 triangle special?
It is a right triangle, and its area is 6.