Calculating the perimeter of common 2D shapes is simple once you learn the formulas. Let’s look at some shapes you probably know.

1. Rectangle:
   To find the perimeter, just add up the lengths of all four sides.
   The formula is:
   P = 2 × (length + width)

   For example, if a rectangle is 4 meters long and 3 meters wide, you would do the math like this:
   P = 2 × (4 + 3) = 2 × 7 = 14 meters

2. Square:
   All sides of a square are the same length. So, to find the perimeter, you can use this formula:
   P = 4 × side

   For example, if each side of the square is 5 cm, the calculation is:
   P = 4 × 5 = 20 cm

3. Triangle:
   To find the perimeter, just add the lengths of all three sides together.
   The formula is:
   P = side₁ + side₂ + side₃

   If the sides of the triangle are 3 m, 4 m, and 5 m, then:
   P = 3 + 4 + 5 = 12 m

4. Circle:
   The perimeter of a circle is called the circumference. You can find it using this formula:
   C = 2πr
   Here, ( r ) is the radius of the circle.

   For a circle with a radius of 3 m, the calculation is:
   C = 2 × π × 3 ≈ 18.85 m

Remembering these formulas can make geometry much easier. Once you get used to them, calculating perimeters will become a piece of cake!