Perimeter of a Square Formula

Geometry Formulas: Area, Volume, Perimeter
Formula:

What is the formula for the perimeter of a square?

Answer

Perimeter of a square
P = 4 · a

Here a is the side (or base). The result comes out in units.

Where the formula comes from

P = 4 · a

Four equal sides, so the outline is the side taken four times. It is the rectangle formula 2(a + b) with b set equal to a.

Worked examples

Let a = 7. Then the perimeter of a square = 28 units.

Let a = 2.5. Then the perimeter of a square = 10 units.

The common mistake

Writing a² instead of 4a. Those are the two square formulas and they answer different questions: 4a fences the plot, a² turfs it.

Other quantities: Square

Related Calculations

See Also

Geometry Formulas: Area, Volume, Perimeter

These are the formulas for the area, perimeter, circumference, volume and surface area of the standard shapes — 31 of them. Each page shows not only the formula but where it comes from, what every letter stands for, two worked examples and the mistake that this particular shape invites. For example, it can help you find out what is the formula for the perimeter of a square? (The answer is: P = 4 · a). Pick the pair — "Area of a circle", for instance — and hit the "Find out" button.
Geometry Formulas: Area, Volume, Perimeter
Formula:

Values from the Formula

If a =Perimeter
14 units
28 units
312 units
416 units
520 units
1040 units

FAQ

What is the formula for the perimeter of a square?

Perimeter of a square P = 4 · a

Where does this formula come from?

Four equal sides, so the outline is the side taken four times. It is the rectangle formula 2(a + b) with b set equal to a.

What is the most common mistake here?

Writing a² instead of 4a. Those are the two square formulas and they answer different questions: 4a fences the plot, a² turfs it.

How do I use this formula?

Put your own numbers in place of the letters. With a = 2.5, for instance, the formula P = 4 · a gives = 10 units.

See Also