Triangle Area Calculator
Find a triangle’s area and perimeter from its three sides.
Area from three sides
You do not need a height or any angles to find a triangle’s area — the three side lengths are enough, thanks to Heron’s formula. This tool applies it directly and also gives the perimeter.
A 3-4-5 triangle has an area of 6 and a perimeter of 12. The tool first checks the triangle inequality, so impossible side combinations are flagged rather than producing a meaningless result.
Reliable and private
It applies Heron’s formula in your browser, so nothing you enter is uploaded.
Frequently Asked Questions
How is the area found?
From the three side lengths using Heron’s formula, which needs no height or angles.
What is Heron’s formula?
Area equals the square root of s times each of s minus a side, where s is half the perimeter.
What if the sides cannot form a triangle?
If any side is longer than the other two combined, no triangle exists, and the tool says so.
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