Trapezoid Area Calculator

How to use this calculator

Enter the two parallel sides and the height (the perpendicular distance between them). The area appears instantly. You can also solve for a missing side or height from a known area.

The formula

A = ½ (a + b) × h

Worked example

A trapezoid with parallel sides of 6 m and 10 m, 4 m apart:

A = ½ × (6 + 10) × 4 = 32 m²

Practical uses

• Irregular plots of land are often split into trapezoids and triangles.
• Open channels and ditches have trapezoidal cross-sections — multiply the area by flow velocity to estimate flow.
• Roof sections and retaining walls are frequently trapezoidal.

Check with a rectangle

If both parallel sides are equal (a = b), the shape is a rectangle and the formula becomes a × h — the same as the rectangle calculator.

Frequently asked questions

What is the area formula for a trapezoid?

Area = ½ × (a + b) × h — the average of the two parallel sides multiplied by the height.

Is a trapezoid the same as a trapezium?

Yes, in most of the world outside North America a four-sided shape with one pair of parallel sides is called a trapezium. In the US it is a trapezoid.

Which height do I use?

The perpendicular distance between the two parallel sides — not the length of a sloping side.

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