Trapezoid Calculator
Calculate the area and perimeter of a trapezoid from its dimensions.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
Can't find what you need?
Request a ToolHow to Use the Trapezoid Calculator
This calculator finds the area and perimeter of a trapezoid from its dimensions.
- Enter the parallel sides. Type the lengths of the top side (a) and bottom side (b). These are the two parallel sides of the trapezoid.
- Enter the height. Type the perpendicular distance between the two parallel sides.
- Optional: enter the leg lengths. If you know the lengths of the non-parallel sides (the left and right legs), enter them to get the perimeter. Without the legs, only the area is calculated.
- Read the results. The area and perimeter (if legs are provided) appear instantly.
The area formula is A = (a + b) / 2 * h, where a and b are the parallel sides and h is the height. The perimeter is a + b + left leg + right leg. The legs are optional because the area depends only on the parallel sides and height.
About Trapezoids
A trapezoid (also called a trapezium in British English) is a quadrilateral with exactly one pair of parallel sides. The parallel sides are called the bases, and the non-parallel sides are called the legs. The height is the perpendicular distance between the bases. If both legs are equal in length, it is called an isosceles trapezoid. Trapezoids appear in architecture (roof trusses, bridge supports), land surveying (irregular lot shapes), and graphic design. The area formula works by averaging the two parallel sides and multiplying by the height, which is equivalent to calculating the area of a rectangle with a width equal to the average of the two bases.
Frequently Asked Questions
What is the formula for the area of a trapezoid?
The area of a trapezoid is A = (a + b) / 2 * h, where a and b are the two parallel sides (bases) and h is the perpendicular height between them. For example, with bases 6 and 10 and height 4, the area is (6 + 10) / 2 * 4 = 32 square units.
Do I need to know the leg lengths to calculate area?
No. The area of a trapezoid depends only on the two parallel sides and the perpendicular height. The leg lengths are needed only for the perimeter calculation. This calculator treats them as optional inputs.
What is an isosceles trapezoid?
An isosceles trapezoid has two equal-length non-parallel sides (legs). The base angles are also equal. A common example is the cross-section of a roof where both sides slope at the same angle.