Add the lengths of all the sides of the shape
Use the same unit for every side
For a rectangle, use the formula Perimeter = 2 × (length + width)
For a square, use the formula Perimeter = 4 × side
For a triangle, use the formula Perimeter = side1 + side2 + side3
For a regular polygon, multiply one side by the number of sides
Write the final answer with the correct unit of measurement