Triangle Angle Calculator
Find all angles from three side lengths using the Law of Cosines.
Formula
cos(A) = (b²+c²-a²)/(2bc)
The Law of Cosines gives each angle opposite its respective side.
Examples
3-4-5 triangle
Equilateral (5-5-5)
7-8-9 triangle
Frequently Asked Questions
How do I find angles from three sides?
Use the Law of Cosines: cos(A) = (b² + c² − a²) / (2bc).
Do the angles always add to 180°?
Yes, the three interior angles of any triangle sum to exactly 180°.
About this Calculator
Find all angles from three side lengths using the Law of Cosines. All calculations are performed in your browser for instant results. Formulas are mathematically exact using JavaScript's built-in Math functions.