How to use the law of sines calculator
Solve a triangle given an angle, its opposite side and a second angle. Enter angle a, side a (opposite a), angle b in the fields above; the side b, angle c, side c are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- A — Angle A (°)
- a — Side a (opposite A)
- B — Angle B (°)
Worked example
With angle a = 40 °, side a (opposite a) = 10, angle b = 60 °, the calculator gives side b ≈ 13.47296; angle c ≈ 80 °; side c ≈ 15.32089.
Frequently asked questions
What is the formula for the law of sines calculation?
Side b = a × sin(B) / sin(A). Angle C (°) = 180-A-B. Side c = a × sin([Angle C]) / sin(A). Here A is angle a (°), a is side a (opposite a), B is angle b (°).
What inputs do I need for the law of sines calculator?
You need angle a in °, side a (opposite a), angle b in °. 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.