Triangle Calculator
Calculate the area, perimeter, and angles of any triangle by entering the three side lengths. Uses Heron's formula and the Law of Cosines.
Enter Side Lengths
Results
Area
6.00
Perimeter
12.00
Type
Scalene
Angles
A
36.9°
B
53.1°
C
90.0°
How the Triangle Calculator Works
Our triangle calculator uses Heron's formula for area and the Law of Cosines for angles. Simply enter all three side lengths to get complete triangle measurements.
Formulas Used
- Area (Heron's) - sqrt(s(s-a)(s-b)(s-c)) where s = (a+b+c)/2
- Angles (Law of Cosines) - cos(A) = (b²+c²-a²) / 2bc
- Perimeter - Sum of all three sides
Triangle Calculator FAQ
How do you calculate the area of a triangle from three sides?▼
Use Heron's formula: Area = sqrt(s(s-a)(s-b)(s-c)), where s is the semi-perimeter (a+b+c)/2, and a, b, c are the three sides.
What makes a valid triangle?▼
A valid triangle must satisfy the triangle inequality theorem: the sum of any two sides must be greater than the third side. All three combinations must be true.
How are the angles calculated?▼
Angles are calculated using the Law of Cosines: cos(A) = (b² + c² - a²) / (2bc). This works for any triangle given all three sides.