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Area of an Obtuse Triangle Calculator.

Calculate the area of an obtuse triangle from its three sides.

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Set your values

Results update as you type.

Area: 5.332682 units²

Area

0.000000units²
Obtuse angle: 117.279613 °

Obtuse angle

0.000000°

Results update automatically as you type.

Use Cases

Geometry homework and exams

Quickly verify your manual calculations for the area of an obtuse triangle when you know all three side lengths.

Example: Check your answer for a triangle with sides 5, 6, and 7.

Real-world measurements

Measure the sides of an obtuse triangular plot or object and compute its area without needing to measure angles.

Example: Find the area of a triangular garden with sides 8 m, 10 m, and 12 m.

Frequently Asked Questions

What is an obtuse triangle?
An obtuse triangle is a triangle with one angle greater than 90 degrees. The other two angles are acute. The area calculation using three sides works for any triangle, including obtuse ones.
How do I use the area of an obtuse triangle calculator?
Simply enter the lengths of side a, side b, and side c in the input fields. The calculator will compute the area using Heron's formula, which requires all three side lengths.
Can I use this calculator for any triangle?
Yes, the formula used (Heron's formula) works for any triangle, whether it is acute, right, or obtuse. However, this calculator is specifically designed for obtuse triangles, so ensure your triangle has an angle greater than 90 degrees.

Tips & Common Mistakes

Tips

  • Ensure the side lengths satisfy the triangle inequality: the sum of any two sides must be greater than the third side. Otherwise, the triangle is invalid.
  • Double-check that your triangle is indeed obtuse. If the largest side squared is greater than the sum of the squares of the other two sides, it's obtuse.
  • Use consistent units for all three sides (e.g., all in meters or all in feet) to get the area in square units.
  • For a quick check, the area of an obtuse triangle is always less than half the product of the two shorter sides.

Common Mistakes to Avoid

  • Entering side lengths that do not form a valid triangle (e.g., 1, 2, 3) – the calculator will not give a meaningful result.
  • Mixing units (e.g., one side in meters and another in centimeters) without converting, leading to incorrect area.
  • Assuming the triangle is obtuse when it might be acute or right – verify the angle condition before using this calculator.

Last updated: August 13, 2026