About the Triangle Calculator
Find the area, perimeter and angles of a triangle from its three sides. This tool is free, works in your browser and needs no sign-up.
How to use the Triangle Calculator
Enter the lengths of the three sides.
Formula used
Heron: Area = √(s(s − a)(s − b)(s − c)) with s = (a + b + c) ÷ 2. Angles come from the law of cosines.
Example
With Side a 3, Side b 4, Side c 5, the calculator shows: Area = 6; Perimeter = 12; Angle A = 36.87°.
Frequently asked questions
Is the Triangle Calculator free to use?
Yes. It is completely free and you can use it as many times as you like.
How accurate is the Triangle Calculator?
The calculator uses standard formulas, so the maths is exact. Real life results can differ because of fees, taxes, rounding or personal factors, so treat the answer as an estimate.
Do you store the numbers I enter?
No. All calculations run in your browser. The values you type are not sent to our server.
Disclaimer: results are estimates for information only. They are not financial, medical or professional advice.