Looking for a triangle calculator area angles from 3 sides? This free tool gives you area, perimeter, all three angles and triangle type from 3 sides. Just enter your numbers and press Calculate — results are instant.
Give three side lengths and this calculator finds the area with Heron's formula: half the perimeter is s, and the area is the square root of s times (s minus each side). The angles come from the law of cosines, which relates each angle to the three sides. It also names the triangle — equilateral, isosceles or scalene — and checks whether it is right-angled. Two sides must add up to more than the third side, or the sides cannot make a triangle at all.
Example: Sides a=3, b=4, c=5
Area: 6.0000
A way to find a triangle's area from its three sides without knowing any angle: take half the perimeter (s), then the area is the square root of s × (s−a) × (s−b) × (s−c).
When the two shorter sides add up to less than the longest side. The sides must satisfy the triangle inequality — any two sides together must be longer than the third.
Check Pythagoras: if the square of the longest side equals the sum of the squares of the other two (like 3² + 4² = 5²), the angle opposite the longest side is exactly 90°.