What is the formula for the perimeter of a parallelogram?

The perimeter is P = 2(a + b), where a and b are the lengths of two adjacent (non-equal) sides. Because opposite sides of a parallelogram are equal, you only need two measurements.

Does it matter which side I enter as a and which as b?

No. Since the formula adds a and b before multiplying by 2, the order does not affect the result.

Can I use this for rectangles and rhombuses?

Yes. Both shapes are special cases of a parallelogram. A rectangle has two distinct side lengths; a rhombus has all sides equal (enter the same value for a and b).

What units does this calculator support?

You can select millimeters, centimeters, meters, kilometers, inches, feet, or yards. The result is displayed in the same unit you choose.

What if both sides are equal?

When a equals b the shape is a rhombus. The perimeter simplifies to P = 4a, and the calculator handles this automatically.

Perimeter of a Parallelogram Calculator

Enter two adjacent side lengths to instantly calculate the perimeter of any parallelogram using P = 2(a + b).

Enter Side Lengths

Side a

Side b

Unit

Enter both side lengths to see the result.

Parallelogram Reference

Formula: P = 2(a + b)

Where:

a — length of one pair of opposite sides
b — length of the other pair of opposite sides
P — perimeter (total boundary length)

Opposite sides of a parallelogram are always equal, so only two distinct measurements are needed.

Summary

A parallelogram is a four-sided polygon where opposite sides are equal in length and parallel to each other. Its perimeter is found with the simple formula P = 2(a + b), where a and b are the lengths of two adjacent sides. This calculator supports any unit of measurement and instantly shows the result as you type.

How it works

Enter the length of side a (one pair of parallel sides).
Enter the length of side b (the other pair of parallel sides).
Choose your preferred unit of measurement.
The calculator applies P = 2(a + b) and displays the perimeter instantly.
Copy the result or reset the inputs to start over.

Use cases

Calculating fencing or border length for parallelogram-shaped plots.
Solving geometry homework and exam problems.
Verifying manual perimeter calculations quickly.
Architecture and design tasks involving parallelogram shapes.
Teaching the perimeter formula to students.
Estimating material needed for framing parallelogram panels.

Frequently Asked Questions

Last updated: 2026-05-25 · Reviewed by Nham Vu