Triangle Calculator
Enter the three side lengths of a triangle to find its perimeter and area, and to classify it by its sides and by its angles. The sides must satisfy the triangle inequality.
Your numbers
Result
- By sides
- Scalene
- By angles
- Right triangle
| Item | Value |
|---|---|
| Sides | 3, 4, 5 |
| Perimeter | 12 |
| Area (Heron) | 6 |
| By sides | scalene |
| By angles | right |
Area from three sides
With all three sides known, Heron’s formula gives the area. Let s be half the perimeter; then area = √[s(s-a)(s-b)(s-c)]. For sides 3, 4, 5: s = 6, and the area is √[6·3·2·1] = 6. The 3-4-5 triangle is also a right triangle.
Types of triangle
By sides: all three equal is equilateral, exactly two equal is isosceles, none equal is scalene. By angles: comparing the longest side to the other two (via c² vs a² + b²) tells you whether it is right (equal), acute (c² smaller) or obtuse (c² larger).
Frequently asked questions
Sources
- Geometry — Heron’s formula and triangle classification
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