Perimeter of a Square Notes

Published on: September 29, 2026

This Perimeter of a Square Calculator finds the distance all the way around a square from the length of one side, and shows the working line by line. Because the four sides match, the side length is counted four times instead of added one at a time. The answer is a length, so it is written in units rather than square units. Following the same pattern every time is what makes the perimeter of a square easy to picture, check, and work out on your own for any side length.

Square with sides labeled a

In the diagram, each side is labeled \(a\).

Step-by-step method

  1. Set up the problem.
  2. Write the formula.
  3. Substitute the side length into the formula.
  4. Work out the perimeter.

Formula:

\(P = 4a\)
See Example 1 Hide Example 1

Problem

\(a = 8\)

Approach

Step-by-step method

  1. Set up the problem.
  2. Write the formula.
  3. Substitute the side length into the formula.
  4. Work out the perimeter.

Step 1

Step 1 - Set up the problem.

In this problem: We are finding the perimeter of a square whose side length is \(a = 8\).

\(a = 8\)

Step 2

Step 2 - Write the formula.

In this problem: The perimeter is the distance all the way around the shape, and a square has four sides of the same length, so that side length is counted four times.

\(P = 4a\)

Step 3

Step 3 - Substitute the side length into the formula.

In this problem: Replacing \(a\) with \(8\) in \(P = 4a\) gives \(P = 4 \times 8\).

\(P = 4 \times 8\)

Step 4

Step 4 - Work out the perimeter.

In this problem: Multiplying the side length by four gives \(4 \times 8 = 32\).

\(P = 4 \times 8 = 32\)

Final Answer

\(P = 32\)
See Example 2 Hide Example 2

Problem

\(a = 2.5\)

Approach

Step-by-step method

  1. Set up the problem.
  2. Write the formula.
  3. Substitute the side length into the formula.
  4. Work out the perimeter.

Step 1

Step 1 - Set up the problem.

In this problem: We are finding the perimeter of a square whose side length is \(a = 2.5\).

\(a = 2.5\)

Step 2

Step 2 - Write the formula.

In this problem: The perimeter is the distance all the way around the shape, and a square has four sides of the same length, so that side length is counted four times.

\(P = 4a\)

Step 3

Step 3 - Substitute the side length into the formula.

In this problem: Replacing \(a\) with \(2.5\) in \(P = 4a\) gives \(P = 4 \times 2.5\).

\(P = 4 \times 2.5\)

Step 4

Step 4 - Work out the perimeter.

In this problem: Multiplying the side length by four gives \(4 \times 2.5 = 10\).

\(P = 4 \times 2.5 = 10\)

Final Answer

\(P = 10\)
See Example 3 Hide Example 3

Problem

\(a = 6\)

Approach

Step-by-step method

  1. Set up the problem.
  2. Write the formula.
  3. Substitute the side length into the formula.
  4. Work out the perimeter.

Step 1

Step 1 - Set up the problem.

In this problem: We are finding the perimeter of a square whose side length is \(a = 6\).

\(a = 6\)

Step 2

Step 2 - Write the formula.

In this problem: The perimeter is the distance all the way around the shape, and a square has four sides of the same length, so that side length is counted four times.

\(P = 4a\)

Step 3

Step 3 - Substitute the side length into the formula.

In this problem: Replacing \(a\) with \(6\) in \(P = 4a\) gives \(P = 4 \times 6\).

\(P = 4 \times 6\)

Step 4

Step 4 - Work out the perimeter.

In this problem: Multiplying the side length by four gives \(4 \times 6 = 24\).

\(P = 4 \times 6 = 24\)

Final Answer

\(P = 24\)
See Example 4 Hide Example 4

Problem

\(a = 4.5\)

Approach

Step-by-step method

  1. Set up the problem.
  2. Write the formula.
  3. Substitute the side length into the formula.
  4. Work out the perimeter.

Step 1

Step 1 - Set up the problem.

In this problem: We are finding the perimeter of a square whose side length is \(a = 4.5\).

\(a = 4.5\)

Step 2

Step 2 - Write the formula.

In this problem: The perimeter is the distance all the way around the shape, and a square has four sides of the same length, so that side length is counted four times.

\(P = 4a\)

Step 3

Step 3 - Substitute the side length into the formula.

In this problem: Replacing \(a\) with \(4.5\) in \(P = 4a\) gives \(P = 4 \times 4.5\).

\(P = 4 \times 4.5\)

Step 4

Step 4 - Work out the perimeter.

In this problem: Multiplying the side length by four gives \(4 \times 4.5 = 18\).

\(P = 4 \times 4.5 = 18\)

Final Answer

\(P = 18\)