Isokinetics Inc. Balance Exercise Ball Chair - Standard or Tall Boy (Exclusive) Frame Height - Choice of Ball Color - Office size 60mm/2.5" Wheels - Adult Size STANDARD HEIGHT ball chair frame with office size 60mm (2.5") wheels, versus 50mm (2") used on other brands. Bigger wheels provide a smoother, quieter rolling experience. Base has 4 wheels, 2 of which are lockable (we recommend placing the lockable wheels in the back to help avoid accidental locking). PLEASE test seating heights (see specific bullet point) at home before you choose between our Standard or Tall Boy frame SITTING HEIGHT. Measurements require ball filled to 52cm (with ball on floor, 20.5" measured straight up to a line level with ball top). Each person is different, but the Standard frame user height range is about 5' 0" to 5' 11". We recommend you test sitting heights at home before buying. In the frame, the ball top is 23.5" unsat on. Seated, a 135 lb person sits about 19.5" off the ground; 150 lb, 19"; 175 lb, 18.5" & 200 lb, 18". By comparison, basic solid seat chairs are 17" to 18" high PLEASE NOTE: Height adapters that add 2" (sold by other sellers) do not fit any model of Isokinetics Inc. brand ball chairs. Please choose between our Standard or Tall Boy frame height IN BOX: Rolling ball base and back in solid black, 4 60mm (2.5") wheels, 2 of which are lockable, a reinforced black metal ball retaining bar, a 52cm Isokinetics Inc. branded ball, a small starter pump, our exclusive ball measuring tape, Isokinetics Inc. Contact and Warranty sheet, assembly instructions and basic exercise guide. We guarantee our ball will inflate to 52cm (20.5"). See our YouTube video on proper ball inflation (search isokinetics inc) Our chairs have a 30 day money back guarantee and a lifetime warranty against manufacturer defects. We also guarantee our 52cm (20.5") ball will fill to its intended size. Read included instructions and watch our YouTube video (search isokinetics inc). Final ball measurement, with ball sitting on the floor, is 52 cm or 20.5" measured straight up from floor to the point level with the ball top. Call us if you have questions