Yes, you do need double the length because there are two sides. So to get one yard of adhesion, you need two yards of tape. I'm going to get 2 yards, Tony wants 2 yards (net yield 1 yard) and Carole wants 1 yard (net yield 1/2 yard), so all we need is one more yard to make the order. George The Third has expressed interest but seems to have a problem with commitment

Once we have a total, I'll place the order, find out how much shipping will be and let everyone know their share, and you can send me your checks. How zat???