📐 Triangle Angle Calculator
Calculate all angles of a triangle
How to Use This Calculator
Select Method
Choose whether you know three sides, two sides and an angle, or two angles.
Enter Values
Input the known measurements based on the selected method.
Calculate
Click "Calculate Angles" to find all three angles.
Verify
Check that the sum of angles equals 180°.
Formula
Law of Cosines (Three Sides):
Angle A = arccos((b² + c² - a²) / (2bc))
Angle B = arccos((a² + c² - b²) / (2ac))
Angle C = 180° - A - B
Law of Sines (Two Sides and Angle):
c = √(a² + b² - 2ab cos(C))
Angle A = arcsin((a sin(C)) / c)
Two Angles:
Angle C = 180° - Angle A - Angle B
About Triangle Angle Calculator
The Triangle Angle Calculator finds all three angles of a triangle using different methods: three sides (Law of Cosines), two sides and an included angle (Law of Sines), or two angles (angle sum property).
When to Use This Calculator
- Geometry: Find missing angles in triangles
- Trigonometry: Apply Law of Cosines and Law of Sines
- Construction: Calculate angles for triangular structures
- Education: Learn triangle angle relationships
Why Use Our Calculator?
- ✅ Multiple Methods: Works with different known values
- ✅ Accurate: Uses precise trigonometric formulas
- ✅ Complete: Finds all three angles
- ✅ Verification: Shows sum equals 180°
- ✅ Free: No registration required
Key Concepts
- Angle Sum: Sum of all angles in a triangle always equals 180°
- Law of Cosines: Used when all three sides are known
- Law of Sines: Used with two sides and an angle
Frequently Asked Questions
What's the sum of angles in a triangle?
Always 180°. This is true for all triangles, regardless of type.
When do I use Law of Cosines vs Law of Sines?
Use Law of Cosines when you know all three sides (SSS) or two sides and the included angle (SAS). Use Law of Sines when you know two angles and a side (AAS/ASA).
Can I calculate with just one angle?
No, you need at least two angles or three sides to find all angles. With one angle, you'd need additional information like side lengths.