Triangle Calculator
Enter three side lengths to verify a triangle, then get perimeter and area using Heron’s formula.
How it works
- 1
Enter your values in the fields.
- 2
Results update automatically as you type.
- 3
Use Reset to clear and try another scenario.
Why use this calculator
- Validity check
- Perimeter and area
- Heron’s formula
- Clear outputs
Triangle inequality
Sides only form a triangle if each side is shorter than the sum of the other two. Invalid inputs are flagged.
Area without height
Heron’s formula uses the semi-perimeter, so you do not need a separate height measurement.
Frequently asked questions
What if sides are invalid?
The tool marks the triangle as invalid and skips meaningful area results.
Which units?
Any consistent unit — results use the same unit squared for area.
Right triangles?
Works for any valid triangle, including right triangles.