Law of Cosines Calculator
Find the third side of a triangle when you know two sides and the angle between them. Enter side a, side b and angle c between them to see side c…
8 of 8 free uses remaining today
Find the third side of a triangle when you know two sides and the angle between them. Enter side a, side b and angle c between them to see side c when you calculate.
Worked example
Example calculated from the starting values. Enter your own values and press Calculate to get your result.
With the default inputs (side a = 5, side b = 7, angle C between them = 60 degrees), the results are: side c 6.2450.
Quick reference: side a vs result
Reference table based on the example values; it is not your calculation result.
| Side a | Side c |
|---|---|
| 2.5 | 6.1441 |
| 5 | 6.2450 |
| 10 | 8.8882 |
| 25 | 22.3383 |
| 50 | 46.8935 |
| 100 | 96.6902 |
Frequently asked questions
What formula does this calculator use?
Side c = sqrt(a^2+b^2-2 × a × b × cos(C × pi ÷ 180)). Variables: a = side a, b = side b, C = angle c between them in degrees.
What do I need to enter?
You need side a, side b, angle c between them (degrees). Results update as you type.
What is an example result?
With the default inputs (side a = 5, side b = 7, angle C between them = 60 degrees), the results are: side c 6.2450.
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