Triangle
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Triangle Calculator Guide
Find a triangle's area and perimeter. Use base and height for a quick area, or enter all three sides to get the area (via Heron's formula), the perimeter, and the triangle type.
Area (base & height) = ½ × base × height. Heron's formula: area = √[s(s−a)(s−b)(s−c)], where s is half the perimeter.
How Do I Find the Area of a Triangle?
If you know the base and height, multiply them and divide by two. A base of 6 and height of 4 gives an area of 12. If you know all three sides, Heron's formula gives the area — a 3-4-5 triangle has an area of 6.
Right, Acute, and Obtuse Triangles
When you enter three sides, the calculator checks the angles. A 3-4-5 triangle is a right triangle because 3² + 4² = 5². If the longest side squared is less than the sum of the other two squared, the triangle is acute; if greater, it is obtuse.
Related: Area Calculator, Circle Calculator, and Square Root Calculator.
Frequently Asked Questions
How do I calculate the area of a triangle?
Multiply the base by the height and divide by two, or use Heron's formula if you know the three side lengths.
What is Heron's formula?
Area = √[s(s−a)(s−b)(s−c)], where a, b, c are the sides and s is half the perimeter.
How do I know if a triangle is a right triangle?
If the square of the longest side equals the sum of the squares of the other two sides, it is a right triangle.
Can any three lengths form a triangle?
Only if each side is shorter than the sum of the other two; otherwise the sides cannot connect.
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