Calculate triangle area and perimeter
40.00
ft²
30.81
ft
15.40
ft
Side a
10.00
ft
Side b
8.00
ft
Side c
12.81
ft
Angle A
51.3°
Angle B
38.7°
Angle C
90°
Area = (base × height) / 2The area of a triangle is half the product of its base and perpendicular height.
Where:
base= The base length of the triangleheight= The perpendicular height from base to opposite vertexPerimeter = base + height + √(base² + height²)When only base and height are provided (no side lengths), the perimeter is estimated using a right triangle approximation.
Where:
base= The base lengthheight= The perpendicular height√(base² + height²)= The hypotenuse (estimated third side)Inputs
Result
Area = (10 × 8) / 2 = 40.00. Perimeter (right triangle approx) = 10 + 8 + √(100 + 64) = 10 + 8 + 12.81 = 30.81. Semi-perimeter = 30.81 / 2 = 15.40.
Inputs
Result
Area = (12 × 5) / 2 = 30.00. Perimeter (right triangle approx) = 12 + 5 + √(144 + 25) = 12 + 5 + 13.00 = 30.00. Semi-perimeter = 30.00 / 2 = 15.00.
Area of a triangle = (base × height) / 2. For example, a triangle with base 10 and height 8 has area = (10 × 8) / 2 = 40 square units. The height must be perpendicular to the base.
Perimeter = side1 + side2 + side3. Simply add all three side lengths. For a triangle with sides 5, 7, and 9, perimeter = 5 + 7 + 9 = 21 units.
Semi-perimeter = (side1 + side2 + side3) / 2, or perimeter / 2. It's used in Heron's formula for calculating area when you know all three sides but not the height.
Yes, using Heron's formula: Area = √[s(s-a)(s-b)(s-c)], where s is the semi-perimeter and a, b, c are the three sides. This works for any triangle when you know all three side lengths.
A triangle's area is calculated using base and height: Area = (base × height) / 2. The height must be perpendicular to the base.
The perimeter is the sum of all three sides. The semi-perimeter is half the perimeter and is used in advanced formulas like Heron's formula.
For right triangles, you can use the Pythagorean theorem to find missing sides: a² + b² = c².
Last Updated: Feb 12, 2026
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