Area of an Obtuse Triangle Calculator
The Area of an Obtuse Triangle Calculator finds the area of a triangle that has one angle greater than 90°. Enter the base and the corresponding height, or use the side-angle-side form. The formula used is: Area = ½ × base × height.
Formula
Area = ½ × base × height
- The Area of an Obtuse Triangle Calculator updates instantly as you change the base or height.
- Formula: Area = ½ × base × height
- Input definitions: • Base: the side you measure the height against • Height: the perpendicular distance from the base to the opposite vertex
- In an obtuse triangle, the height to the longest side falls inside the triangle, but the height to a shorter side may land outside it.
- The height must be perpendicular to the chosen base, not the length of another side.
- Area and lengths share the same unit (area is that unit squared).
Example Calculation
Inputs
- Base: 10
- Height (perpendicular to base): 4
For a base of 10 and a perpendicular height of 4: Area = ½ × 10 × 4 = 20 square units.
Frequently asked questions
What is an obtuse triangle?
It is a triangle with one interior angle greater than 90°. The side opposite that angle is the longest side.
How do I find its area?
Use the base and the perpendicular height: Area = ½ × base × height, the same formula as any triangle.
Why can the height fall outside the triangle?
For an obtuse triangle, the perpendicular from a vertex to a shorter side may land beyond the side, so the height is measured to the extended base line.
What if I only know two sides and an angle?
Use Area = ½ × a × b × sin(C) with the two sides and the included angle, which works for obtuse triangles too.
What if I know all three sides?
Use Heron's formula to find the area directly from the three side lengths.