When you call us to rent a fence, one of the first things we’ll ask is how much fence you need in linear footage. Some callers give us the area they are trying to enclose, assuming we can calculate the footage based on that. That would surely make things simpler but the fact is, spaces with the same area, will have differing perimeters depending on the shape of the space.
Following are some examples. As you can see, depending on the shape of the rectangle, the perimeter, and therefore the quantity of fencing can vary widely.
From learnzillion.com