Trapezoid Area Calculator

A trapezoid is a quadrilateral with one pair of parallel sides. Its area can be found from the lengths of the two parallel sides (top and bottom bases) and the height.

Enter the top base, bottom base, and height to instantly calculate the area of a trapezoid. Often used to find site areas in architecture and civil engineering.

For example, a trapezoid with top base 4 cm, bottom base 8 cm, and height 5 cm has an area of 30 cm².

Trapezoid Area Calculator Calculation Method

a: top base, b: bottom base, h: height

The area is 0 .

About This Calculator

A trapezoid (trapezium in British English) is a quadrilateral with at least one pair of parallel sides. Its area is the average of the two parallel sides multiplied by the height between them.

Enter the two parallel sides and the perpendicular height to calculate the area.

The trapezoid formula averages the two parallel sides and multiplies by the height: A = (a + b) / 2 × h. Parallel sides of 8 and 12 with height 5 give 50, exactly the area of a 10 × 5 rectangle. Korean mathematics defines a trapezoid as having exactly one pair of parallel sides, while some curricula also admit parallelograms.

Key Formula:Area = (a + b) / 2 × h

Frequently Asked Questions

What is the difference between a trapezoid and a parallelogram?

A parallelogram has two pairs of parallel sides; a trapezoid has only one pair (under the exclusive definition). Every parallelogram is a trapezoid under the inclusive definition, but not the reverse.

How do I find the height of a trapezoid from its area?

Rearrange the formula: h = 2A / (a + b). For an area of 60 with parallel sides of 8 and 12, the height is 120 / 20 = 6.

What happens when the parallel sides are equal?

The formula collapses to a × h, the rectangle or parallelogram case. Every correct generalisation should reduce to the simpler shape like this, which makes a useful check.

How do I find the height from the area?

Rearrange to h = 2A / (a + b). An area of 50 with parallel sides 8 and 12 gives 100 / 20 = 5.

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Sources & last update

2026-10-19