How do you work out the perimeter of a pentominoe?

To calculate the perimeter of a pentomino, first, determine its shape by counting the number of unit squares that make up the figure. Then, trace the outline of the pentomino and count the total length of its edges. Each edge that borders the outside contributes to the perimeter, while edges that touch other squares do not. Finally, sum the lengths of the outer edges to find the total perimeter.