The formula for the perimeter of a shape depends on the type of shape you're dealing with. Below are the perimeter formulas for some common shapes:

1. Perimeter of a Rectangle:
   $P = 2 \times (l + w)$ where $l$ is the length and $w$ is the width.

2. Perimeter of a Square:
   $P = 4 \times s$ where $s$ is the side length.

3. Perimeter of a Triangle:
   $P = a + b + c$ where $a$, $b$, and $c$ are the lengths of the three sides.

4. Perimeter of a Circle (Circumference):
   $P = 2 \times \pi \times r$ where $r$ is the radius.

5. Perimeter of a Regular Polygon:
   $P = n \times s$ where $n$ is the number of sides and $s$ is the length of one side.

Would you like more details on a specific shape's perimeter, or have any questions?

Here are 5 related questions:

1. How do you find the perimeter of irregular shapes?
2. How does the perimeter formula change for composite shapes?
3. What is the difference between perimeter and area?
4. How is the perimeter of an ellipse calculated?
5. Can you derive the perimeter formula for a trapezoid?

Tip: Always make sure the units of all dimensions are the same before calculating the perimeter!