Purpose: Enter three sides to get the triangle's area, perimeter, angles and type (equilateral, isosceles, scalene, right).
Triangle Calculator
The Triangle Calculator finds the area, perimeter, angles, and unknown sides of any triangle using proven methods - Heron's formula, and the SSS, SAS, and ASA rules.
Which method to use
- SSS (three sides known) - finds all three angles and the area.
- SAS (two sides and the included angle) - finds the third side, the area, and the remaining angles.
- ASA (two angles and the side between them) - finds the remaining side lengths.
Heron's formula for area
When all three sides (a, b, c) are known, the area is found with Heron's formula: first the semi-perimeter s = (a + b + c) / 2, then area = √(s(s−a)(s−b)(s−c)). The calculator also checks the triangle inequality, so it warns you if three lengths cannot actually form a triangle.
Frequently Asked Questions
What is Heron's formula?
It calculates a triangle's area from its three side lengths using the semi-perimeter, without needing the height: area = √(s(s−a)(s−b)(s−c)).
Can it find angles from three side lengths?
Yes. With all three sides (SSS) it uses the law of cosines to compute every interior angle.
What does the triangle inequality check do?
It confirms that the sum of any two sides is greater than the third. If not, the three lengths cannot form a real triangle and the tool tells you.
Does it work for right, isosceles, and scalene triangles?
Yes. The methods apply to every triangle type, including right-angled, isosceles, equilateral, and scalene.
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