Triangle Calculator
Solve any triangle from three known values (SSS, SAS or ASA): all sides, angles, area, perimeter and heights, using the law of sines and cosines.
How to use
- 1Choose what you know: three sides, two sides and the angle between them, or two angles and the side between them.
- 2Enter the values (angles in degrees).
How it's calculated
Law of cosines: c² = a² + b² − 2ab cos C. Law of sines: a ÷ sin A = b ÷ sin B = c ÷ sin C. Area by Heron's formula: √(s(s − a)(s − b)(s − c)), s = half the perimeter.
Frequently asked questions
Why isn't SSA an option?
Two sides and a non-included angle can give two different triangles (the ambiguous case). Use SSS, SAS or ASA for a unique answer.
What makes three sides a valid triangle?
Each side must be shorter than the other two combined (the triangle inequality).
How do I know if a triangle is right-angled?
If a² + b² = c² for the longest side c. The calculator reports the triangle type.