Our bands are all the same size but they
come in five strength levels.  X-Light: 2.5-4.5kgs (5-10lbs)Light: 4.5-7kgs (10-15lbs)Medium: 7-9kgs (15-20lbs)Heavy: 11-13.5kgs (25-30lbs)X-Heavy: 13.5-18kgs (30-40lbs)