Trapezoid Calculator

Calculate the area, midsegment and perimeter of a trapezoid from its parallel bases, height and side lengths

Your result will appear here.

About the Trapezoid Calculator

Trapezoid Calculator finds area and related measurements for a quadrilateral with one pair of parallel sides under the usual definition. It is useful for geometry exercises, land sections, channels and shapes that taper from one width to another.

The area depends on the two parallel bases and the perpendicular height between them. Slanted side length is not a substitute for height unless it is actually perpendicular to the bases.

How to Use the Trapezoid Calculator

  1. Enter the lengths of the two parallel bases.
  2. Enter the perpendicular height.
  3. Add non-parallel side lengths if perimeter is required.
  4. Calculate area or perimeter and verify the height is measured at a right angle to the bases.

How the Calculation Works

Trapezoid area A = (a+b)h/2, where a and b are the parallel sides and h is their perpendicular separation.

Perimeter is the sum of all four side lengths. For special isosceles or right trapezoids, missing sides may be derived with right-triangle relationships when enough dimensions are known.

Worked example

Trapezoid Calculator Worked Example

Bases 8 m and 14 m with height 5 m

Area = (8+14)×5÷2 = 22×2.5 = 55 m².

Result guide

Understanding Your Trapezoid Calculator Result

The formula effectively multiplies height by the average of the two parallel side lengths. It does not require the two non-parallel sides to be equal.

Before you rely on the answer

Assumptions and Limitations

  • The selected sides a and b are parallel.
  • Height is perpendicular to the bases.
  • The shape is planar and measurements use compatible units.

Practical tip

Using This Result in Practice

For site or fabrication measurements, do not use a diagonal or sloping side as the height unless it is perpendicular. A small angle error can materially change the computed area.

Related calculations

Useful Calculations to Continue With

If the project shape combines trapezoids with rectangles or triangles, use the Area Calculator for the component sections.

If both pairs of opposite sides are parallel, use the Parallelogram Calculator instead.

Common questions

Trapezoid Calculator FAQ

What is the trapezoid area formula?

A=(a+b)h/2.

Can the slanted side be used as height?

Only if it is perpendicular to the parallel bases.

Do the non-parallel sides have to be equal?

No. That is only true for an isosceles trapezoid.