Formula
Perimeter is the path around the triangle:
Perimeter = side A + side B + side C
The triangle page uses the same three sides to find area. A rectangle's perimeter is on the rectangle page.
Assumptions
- The three lengths can form a triangle.
- Each side is a straight edge.
Worked example
Sides 3, 4, and 5 have a perimeter of 12.
Input definitions
- Sides
- The three edge lengths.
Limitations
Results are rounded for display. This is a classroom calculation, not a measurement from a lab or a financial filing.
Questions
Why reject some side lengths?
Two sides must be longer together than the third, or they cannot close a triangle.
Where is the area?
The triangle calculator uses Heron's formula on the same kind of sides.