Area of an Oblique Triangle Calculator


Area of an Oblique Triangle Calculator

Welcome, geometry enthusiasts! If you thought oblique triangles were just for making your geometry textbook look like a dangly earring, you’re in for a surprise! They have an area (yes, really!) and we’re going to show you how to calculate it. But brace yourself, it’s going to be a trigonometrical roller coaster!

The formula to calculate the area of an oblique triangle is:

Area = 0.5 * a * b * sin(C)

Where a and b are the lengths of two sides and C is the angle between them.

Categories of Oblique Triangles

Category Range
Small 0 – 0.5 sq ft
Medium 0.5 – 1 sq ft
Large 1+ sq ft

Calculation Examples

Individual Side A (ft) Side B (ft) Angle C (degrees) Area (sq ft) Calculation
Sherlock 3 4 60 6 0.5 * 3 * 4 * sin(60)
Watson 5 7 45 12.5 0.5 * 5 * 7 * sin(45)

Calculation Methods

Method Advantages Disadvantages Accuracy
Trigonometric Most Accurate Requires Calculator High
Graphic Visual Less Accurate Medium

Evolution of Concept

Time Concept
Ancient Area as field size
Modern Trigonometric Calculation


  1. Measurement Errors: Small errors in measurement can lead to large errors in area calculation.
  2. Round-off Errors: Calculations involving square roots and trigonometric functions can lead to round-off errors.


Method Pros Cons
Graphic Visual Less Accurate


  1. What is an oblique triangle? An oblique triangle is a triangle that is not a right triangle.
  2. How is the area of an oblique triangle calculated? The area is calculated using the formula 0.5 * a * b * sin(C).
  3. What is the difference between oblique and right triangle? A right triangle has one 90-degree angle, whereas an oblique triangle has no 90-degree angles.
  4. Can I calculate the area of an oblique triangle without knowing the height? Yes, you can use the trigonometric formula given above.
  5. What are some practical uses of oblique triangle calculations? They are used in various fields like architecture, construction, and physics.
  6. Can I use any angle for ‘C’ in the formula? ‘C’ should be the angle between sides ‘a’ and ‘b’.
  7. Why are there errors in calculating the area of oblique triangles? Errors can occur due to inaccurate measurements and round-off errors during calculations.
  8. Are there alternatives to the trigonometric method for calculating the area of oblique triangles? Yes, one alternative is the graphical method, but it is less accurate.
  9. What are the categories of oblique triangles based on area? The categories are small (0 – 0.5 sq ft), medium (0.5 – 1 sq ft), and large (1+ sq ft).
  10. What resources can I refer to for more on oblique triangle calculations? You can refer to the National Institute of Standards and Technology and the Mathematics Department, University of California.


  1. National Institute of Standards and Technology – Provides standards and guidelines for mathematical calculations. Link
  2. Mathematics Department, University of California – Offers comprehensive mathematical resources and research. Link