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Area of an Oblique Triangle Calculator.

Calculate triangle area from two sides and their included angle.

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Results update as you type.

Area: 15.155445 units²

Area

15.155445units²

Results update automatically as you type.

Use Cases

Land Surveying and Plot Measurement

Quickly estimate the area of a triangular plot of land when you know two side lengths and the angle between them, without needing to measure the height.

Example: A triangular field has sides of 150 m and 200 m with an included angle of 60°.

Geometry Homework and Exam Prep

Verify your manual calculations for triangle area problems in trigonometry or geometry, especially when dealing with non-right triangles.

Example: Find the area of a triangle with sides 7 cm and 9 cm and included angle 45°.

Frequently Asked Questions

How do I calculate the area of an oblique triangle with this calculator?
Enter the lengths of two sides (Side a and Side b) and the measure of the included angle (the angle between those two sides) in degrees. The calculator uses the formula: Area = 0.5 * a * b * sin(angle).
What is an oblique triangle?
An oblique triangle is any triangle that does not contain a right angle (90°). It can be acute (all angles less than 90°) or obtuse (one angle greater than 90°). This calculator works for any oblique triangle when you know two sides and the included angle.
Can I use this calculator for right triangles?
Yes, you can use it for right triangles as well. If the included angle is 90°, the formula simplifies to 0.5 * a * b, which is the standard area formula for a right triangle. However, the calculator is specifically designed for oblique triangles.

Tips & Common Mistakes

Tips

  • Ensure the included angle is the angle between the two sides you enter. If you have a different angle, use the Law of Cosines to find the needed angle first.
  • The angle must be in degrees. If your angle is in radians, convert it to degrees by multiplying by 180/π.
  • Double-check that your side lengths are in the same unit (e.g., both in meters or both in feet) to get the area in square units.
  • For a quick sanity check, remember that the area will be between 0 and 0.5 * a * b. If your result is outside this range, recheck your inputs.

Common Mistakes to Avoid

  • Entering the angle in radians instead of degrees. The calculator expects degrees, so convert if necessary.
  • Using the wrong angle – the included angle must be the angle between the two given sides, not any other angle of the triangle.
  • Forgetting to use the same units for both sides, which leads to an incorrect area unit (e.g., mixing meters and centimeters).

Last updated: August 13, 2026