Law of Cosines Calculator
Find unknown sides or angles in any triangle using the law of cosines
About this calculator
The Law of Cosines Calculator helps you find unknown sides or angles in any triangle when you know at least three measurements. This powerful tool applies the mathematical relationship c² = a² + b² - 2ab cos(C) to solve triangle problems that can't be handled by basic trigonometry. It's essential for students, engineers, surveyors, and anyone working with non-right triangles in geometry, physics, or real-world applications like construction and navigation.
How to use
Enter any three known values from your triangle: either three sides, two sides and the included angle, or two angles and one side. Select the appropriate input fields and enter your measurements. Click calculate to instantly find the missing sides or angles using the law of cosines formula.
Frequently asked questions
When should I use the law of cosines instead of other triangle formulas?
Use the law of cosines when you have three sides, or two sides with their included angle. It works for any triangle type.
Can this calculator work with obtuse triangles?
Yes, the law of cosines works perfectly with acute, right, and obtuse triangles, making it more versatile than basic trigonometry.
What units can I use for measurements?
You can use any units (inches, feet, meters, etc.) as long as all measurements use the same unit consistently.