To determine how many flags you need for your pool, determine the width of your pool in inches and divide by 13. This should be your number of flags. For example, a 54 foot wide pool is 648 inches. Divide by 13 to get 49.84.... You may round down to 48, 49 or up to 50 flags. You may also select fewer flags as ideally you should have just enough flags to be seen.