Exercise balls usually come in 5 sizes and can be selected according to your height..
| Exercise ball diameter | Person’s height |
| 45 cm | 5′ and under |
| 55 cm | 5’1″– 5’8″ |
| 65 cm | 5’9″– 6’2″ |
| 75 cm | 6’3″– 6’7″ |
| 85 cm | 6’8″ and taller |
When sitting on the ball with your feet flat on the floor your knees should be level with or slightly lower than your hips.
Because the exercise balls are flexible weight is also an important factor. If you have higher than average body weight the exercise ball will compress down when you sit on it so you may want to try the next larger size.
Exercise balls can be made larger or smaller depending on how much you air you fill them with. However, keep in mind that releasing air from an exercise ball will make it more stable which will make exercising on it easier and may cause some of your exercises to be less effective.
