Triangle Calculator — Area, Perimeter & Angles (SSS)
Quick answer: Enter three side lengths to find area, perimeter, angles, and whether the triangle is equilateral, isosceles, or scalene.
Enter the three side lengths of any triangle to instantly calculate area (via Heron's formula), perimeter, all three interior angles (using the Law of Cosines), and the triangle type (equilateral, isosceles, or scalene).
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Last reviewed: April 2026Report an error
Enter all three side lengths to calculate area, perimeter, and angles (SSS method).
Area
6
Area = 6, Perimeter = 12. Type: scalene right triangle. Angles: A=36.8699°, B=53.1301°, C=90°.
Area
6
Perimeter
12
Angle A
36.8699°
Angle B
53.1301°
Angle C
90°
Type
scalene (right)
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How to Use This Triangle Calculator Calculator
- 1Enter side a.
- 2Enter side b.
- 3Enter side c.
- 4Read area, perimeter, all three angles, and triangle type.
Frequently Asked Questions
- Heron's formula finds triangle area from side lengths: A = √(s(s-a)(s-b)(s-c)), where s = (a+b+c)/2 is the semi-perimeter.
- For three lengths to form a triangle, each side must be less than the sum of the other two: a+b>c, a+c>b, b+c>a. If any condition fails, no triangle exists.
- Use the Law of Cosines: cos(A) = (b²+c²−a²)/(2bc). Solve for angle A in degrees using arccos.
- All three sides equal. All three angles = 60°. Area = (√3/4)s².
- Area = (base × height) / 2 = (leg₁ × leg₂) / 2. The two legs are the base and height.
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