Triangle Area Calculator
Calculate the area of any triangle. Use base and height, the three side lengths with Heron's formula, or two sides and the angle between them.
How to find the area of a triangle
- Pick the method that matches the values you know.
- Enter the base and height, the three sides, or two sides and the included angle.
- Read the area, plus the perimeter when all three sides are known.
Examples
Base and height
base = 10, height = 4
area = 20
Heron's formula (3-4-5 triangle)
a = 3, b = 4, c = 5
area = 6, perimeter = 12
Two sides and the angle (SAS)
sides 5 and 7, angle 30 degrees
area = 8.75
Frequently asked questions
What is the formula for the area of a triangle?
The base and height formula is one half times base times height. Heron's formula and the SAS formula give the same area from sides or from two sides and an angle.
What is Heron's formula?
With sides a, b and c, let s be half the perimeter. The area equals the square root of s times (s minus a) times (s minus b) times (s minus c).
How does the SAS method work?
When you know two sides and the angle between them, the area equals one half times side a times side b times the sine of the included angle.
Why does it reject some side lengths?
Three lengths only form a triangle if each pair of sides adds up to more than the third side. Values that break this triangle inequality are rejected.
Do angles use degrees or radians?
The SAS method takes the included angle in degrees, so 30 means 30 degrees. It is converted to radians internally before the sine is taken.
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