What is the formula for the perimeter of a rectangle?

The perimeter P of a rectangle is calculated as P = 2 * (length + width). This adds all four sides: two lengths and two widths.

What units does this calculator support?

You can select millimeters (mm), centimeters (cm), meters (m), kilometers (km), inches (in), feet (ft), yards (yd), or miles (mi). The result is shown in the same unit you choose.

Can I use decimal values?

Yes. The calculator accepts any positive decimal number. For example, a length of 3.75 ft and a width of 2.5 ft gives a perimeter of 12.5 ft.

What is the perimeter of a square?

A square is a special rectangle where length equals width, so its perimeter is 4 * side. Enter the same value in both fields to calculate a square's perimeter.

What happens if I enter zero or a negative number?

The calculator will display an error message. Both length and width must be positive numbers greater than zero.

Is the calculation done on my device or on a server?

All calculations run entirely in your browser. No data is sent to any server.

Perimeter of a Rectangle Calculator

Name: Perimeter of a Rectangle Calculator
Availability: InStock
Author: Nham Vu

Enter a rectangle's length and width to instantly calculate its perimeter using P = 2 * (l + w).

Rectangle Dimensions

Unit

Length

Width

Result

Enter length and width to see the perimeter.

Perimeter

Diagram

Measurement	Value
Length
Width
Perimeter

Summary

Enter a rectangle's length and width to instantly calculate its perimeter using P = 2 * (l + w).

How it works

Enter the rectangle's length in the first input field.
Enter the rectangle's width in the second input field.
Choose your preferred unit of measurement from the dropdown.
The perimeter is calculated instantly using P = 2 * (length + width).
Copy the result or clear the fields to start a new calculation.

Use cases

Determine how much fencing is needed to enclose a rectangular yard.
Calculate the amount of trim or baseboard required for a rectangular room.
Find the total border length of a rectangular garden bed.
Compute picture-frame or mat-board perimeter for custom framing.
Solve geometry homework problems involving rectangle perimeters.
Estimate ribbon or edging material needed for rectangular decorations.

Frequently Asked Questions

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