Law of Cosines Calculator

Last updated: April 5, 2026

Solve for

Side a

Side b

Angle C (degrees)

Side c

6.244998

Calculator by CalculatorNut

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How to Use

Pick mode: solve side c from two sides and included angle, or angle C from three sides.

Formula

c² = a² + b² − 2ab cos(C); cos(C) = (a² + b² − c²)/(2ab)

FAQ

Radians?: Angles are entered in degrees here.
Obtuse angles?: Works for obtuse C as long as sides form a valid triangle.
Law of sines?: Use when you have AAS/ASA patterns—different tool.

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