Gym Ball Load Ratings Static Load Capacity: 550 lbs / 250 kg Dynamic Load Capacity: 450 lbs / 200 kg Size Chart (Ball Diameter> User Height): 45cm/18in> 5"0"/152cm 55cm/22in> 5"1" - 5"6"/155 -167cm 65cm/26in> 5"7" - 6"1"/170 - 185cm 75cm/30in> 6"2" - 6"8"/188cm - 202cm The height guidelines shown are only suggestions. Some therapists, trainers and midwifes may suggest that you use an alternative size. Helps Improve Balance, Coordination and Flexibility. Ideal for Core Strength Training, Stretching, Toning, Resistance Exercises. FAQs: Q1: The nozzle doesn"t fit, I can"t use the pump. A: The inserted white plug (air stopper) on the ball must be removed first! Inflation Instruction: Step 1: Take out the inserted white plug (air stopper) from the ball Step 2: Insert the tip of the pump into the mouth (built-in variable aperture) Step 3: Pumping the ball to proper size (usually 10 minutes for a 75cm ball) Step 4: Quickly replace the white plug back into the hole to stop air leak. Done! Q2: Ball size is smaller than advertised. A: Ball is made of rubber which will become much contracted being packed tightly into the box. Thus, keep pumping to stretch the rubber is the key. If it is hard to reach suggested ball size during 1st inflation, users can leave the ball as it is for a day, and then pump again after the PVC material gets fully stretched. Q3: The pump doesn"t pump out air. How to get a replacement for a faulty pump, or a ball? A: Please "Contact Seller" directly (other than Amazon Customer Service) from Amazon Buyer Central against this order for a replacement or refund. Seller aims to provide hassle-free service and usually replies most emails in 12 hours.