Law of Cosines Calculator
Find the third side of any triangle from two sides and the angle between them using the law of cosines.
Formula: c = √(a² + b² − 2ab × cos C)
About Law of Cosines Calculator
Law of Cosines Calculator is a free online calculator that gives you an instant, accurate result as you type. Find the third side of any triangle from two sides and the angle between them using the law of cosines.
The calculation uses the standard formula c = √(a² + b² − 2ab × cos C) 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.
The law of cosines generalizes the Pythagorean theorem: when the angle C is 90°, cos C is zero and the formula becomes c² = a² + b².
Frequently Asked Questions
Is Law of Cosines Calculator free to use?
Yes. Law of Cosines 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 (c = √(a² + b² − 2ab × cos C)) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
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