What is the formula for the perimeter of a trapezoid?

The perimeter equals the sum of all four sides: P = a + b + c + d, where a and b are the two parallel bases and c and d are the two legs (non-parallel sides).

Does it matter which sides are the bases and which are the legs?

For the perimeter calculation it does not matter — all four sides are simply added together. The distinction between bases and legs matters for area calculations, not perimeter.

What units does this calculator use?

The calculator is unit-agnostic. Enter measurements in any consistent unit (cm, m, inches, feet, etc.) and the result will be in the same unit.

Can I calculate the perimeter of an isosceles trapezoid?

Yes. For an isosceles trapezoid the two legs are equal, so enter the same value for c and d. The calculator handles all trapezoid types.

What is the difference between a trapezoid and a trapezium?

In American English a trapezoid has exactly one pair of parallel sides. In British English the same shape is called a trapezium. This calculator works for both definitions.

Perimeter of a Trapezoid Calculator

Enter the four side lengths of a trapezoid to instantly calculate its perimeter.

Side Lengths

Enter all four sides in the same unit (cm, m, in, ft, etc.).

a — Bottom Base

b — Top Base

c — Left Leg

d — Right Leg

Result

Enter the four side lengths and press Calculate.

Summary

A trapezoid (also called a trapezium) is a quadrilateral with at least one pair of parallel sides. Its perimeter is simply the sum of all four side lengths: P = a + b + c + d, where a and b are the parallel bases and c and d are the non-parallel legs. This calculator lets you enter any four positive side lengths and computes the perimeter instantly.

How it works

Enter the length of the first parallel base (a).
Enter the length of the second parallel base (b).
Enter the length of the left leg (c).
Enter the length of the right leg (d).
The perimeter is calculated instantly as P = a + b + c + d.
Copy the result or reset the inputs to start over.

Use cases

Calculate fencing required around a trapezoidal plot of land.
Find the border length of a trapezoidal tile or paving slab.
Solve geometry homework involving trapezoid perimeters.
Check manual calculations quickly during construction projects.
Compute trim length needed for a trapezoidal window or frame.
Verify answers in standardized math tests and quizzes.

Frequently Asked Questions

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