How to use the triangle angles from sides calculator
Find all angles of a triangle from its three sides (law of cosines). Enter side a, side b, side c in the fields above; the angle a, angle b, angle c are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- a — Side a
- b — Side b
- c — Side c
Worked example
With side a = 5, side b = 6, side c = 7, the calculator gives angle a ≈ 44.41531 °; angle b ≈ 57.12165 °; angle c ≈ 78.46304 °.
Frequently asked questions
What is the formula for the triangle angles from sides calculation?
Angle A (°) = acos((b × b+c × c-a × a) / (2 × b × c)). Angle B (°) = acos((a × a+c × c-b × b) / (2 × a × c)). Angle C (°) = 180-[Angle A]-[Angle B]. Here a is side a, b is side b, c is side c.
What inputs do I need for the triangle angles from sides calculator?
You need side a, side b, side c. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.