A trapezoid (also called a trapezium in British English) is a four-sided polygon with exactly one pair of parallel sides, called the bases.

What is the formula for the area of a trapezoid?

The area formula is A = (a + b) / 2 × h, where a and b are the lengths of the two parallel bases and h is the perpendicular height between them.

Does the height mean the slant side length?

No. The height h is the perpendicular distance between the two parallel bases, not the length of the slanted leg. Use trigonometry if you only know the leg length and angle.

Can I use decimal values?

Yes. The calculator accepts decimal inputs for all three values and rounds the result to four decimal places for precision.

What units does this calculator use?

The calculator is unit-agnostic. Enter values in any consistent unit (cm, m, ft, in, etc.) and the result will be in the corresponding square unit.

Area of a Trapezoid Calculator

Calculate the area of a trapezoid instantly by entering its two parallel sides and height.

Enter Dimensions

All three fields are required. Use any consistent unit.

Base a (first parallel side)

Base b (second parallel side)

Height h (perpendicular distance)

Unit label (optional)

Area

—

Enter values and press Calculate

Formula

A = (a + b) / 2 × h

Summary

This calculator computes the area of a trapezoid using the standard formula A = (a + b) / 2 × h, where a and b are the lengths of the two parallel sides (bases) and h is the perpendicular height. Results update instantly as you type. Supports decimal inputs and displays a labeled diagram for clarity.

How it works

Enter the length of the first parallel side (base a).
Enter the length of the second parallel side (base b).
Enter the perpendicular height (h) between the two bases.
The area is calculated instantly using A = (a + b) / 2 × h.
Optionally change the unit label to match your measurement system.

Use cases

Calculating land or floor area with trapezoidal shapes.
Architecture and construction material estimation.
Geometry homework and exam preparation.
Verifying manual calculations quickly.
Engineering cross-section area calculations.
Garden or field area planning with irregular boundaries.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu