Law of Sines Calculator
Find an unknown triangle side from a known side and its opposite angle plus the angle opposite the unknown side.
Formula: b = a × sin B / sin A
About Law of Sines Calculator
Law of Sines Calculator is a free online calculator that gives you an instant, accurate result as you type. Find an unknown triangle side from a known side and its opposite angle plus the angle opposite the unknown side.
The calculation uses the standard formula b = a × sin B / sin A and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
In any triangle, the ratio of a side to the sine of its opposite angle is the same for all three sides — it equals the diameter of the circumscribed circle.
Frequently Asked Questions
Is Law of Sines Calculator free to use?
Yes. Law of Sines Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (b = a × sin B / sin A) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
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