Triangle Angle Calculator

Calculate missing triangle angles. Free online triangle angle finder calculator.

The Triangle Angle Calculator finds missing angles in any triangle. Since triangle angles always sum to 180°, enter two angles to find the third, or use side lengths with trigonometry to find all angles. Essential for geometry problems, construction, and any application requiring triangle angle calculations.

Common use cases

  • Geometry homework
  • Construction angle cuts
  • Surveying calculations
  • Design and drafting
  • Navigation problems

How to use

  1. Enter known angles (1 or 2)
  2. Or enter all three side lengths
  3. Click calculate for missing angle(s)
  4. View the angle sum verification
  5. See the calculation method used

FAQ

Why do triangle angles sum to 180°?

This is a fundamental property of Euclidean geometry, provable by extending a side and using parallel line properties.

How do I find angles from sides?

Use the Law of Cosines: cos(A) = (b² + c² - a²)/(2bc), then solve for angle A.

What is an obtuse triangle?

A triangle with one angle > 90°. The other two angles must be acute (< 90°).

Can a triangle have two right angles?

No, that would sum to 180° already, leaving 0° for the third angle—impossible.