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A trapezoid's area depends on both of its parallel sides, not just one — averaging them together before multiplying by the height is the key idea behind the formula.
This calculator finds a trapezoid's area directly from its two parallel side lengths and its height, with a full step-by-step solution.
How it works
Enter the lengths of the two parallel sides (a and b) and the perpendicular height between them. The calculator averages the two parallel sides and multiplies by the height to find the area.
- Enter parallel side a.
- Enter parallel side b.
- Enter height.
- Click Calculate to see your results.
Examples
A trapezoid with sides 8 and 12, height 5
A trapezoid with parallel sides of 8 and 12 and a height of 5 has an area of 50.
Who should use it
- Calculating the area of a trapezoidal garden bed, plot of land, or room.
- Solving trapezoid area problems for geometry coursework.
Industry applications
- Land surveying and landscaping
- Geometry and construction education
Advantages
- Simple, exact formula with no approximation.
- Includes a complete, formula-based step-by-step solution.
Limitations
- Requires knowing the true perpendicular height, which isn't always directly given in a real-world measurement.
Common mistakes to avoid
- Using the length of a slanted (non-parallel) side as the height instead of the true perpendicular distance between the parallel sides.
- Averaging the parallel sides incorrectly, or forgetting to average them at all before multiplying by the height.
Best practices
- Make sure the height you enter is the perpendicular distance between the two parallel sides, not the length of a slanted side.
Tips
- If you know the trapezoid's four side lengths but not the height directly, you may need to use the Pythagorean theorem on the non-parallel sides first to find the perpendicular height.