Triangle Calculator
Solve any triangle from three known values (sides and angles): all sides, angles, area, perimeter and heights.
About the Triangle Calculator
Enter any three of the six values, with at least one side, and leave the rest blank. Angle A is opposite side a, B opposite b and C opposite c.
Three sides (SSS), two sides and the angle between them (SAS), or two angles and a side (ASA, AAS) always give one triangle. Two sides and an angle not between them (SSA) can give two, and the calculator tells you when that happens.
The formula
Law of cosines: c² = a² + b² − 2ab·cos C; Law of sines: a/sin A = b/sin B = c/sin C
- Area
- ½ab·sin C
- Angles
- A + B + C = 180°
Worked example
Sides 3, 4, 5
- C = 90° (a right triangle)
- Area = ½ × 3 × 4 = 6
Questions people ask
Why can't I enter three angles?
Angles alone fix the shape but not the size; you need at least one side.
What's the ambiguous case?
With SSA, the known side can swing to two positions, giving two valid triangles.