Each model comes in different sizes because people come in different sizes. Making sure that your pogo stick fits you properly is important. Proper fit will provide a safer, more comfortable ride and allow you to get optimum performance from your pogo. Proper sizing is based only on a riders height, not weight. There is some overlap between sizes to account for different types of bodies. If you are near the top of a size range and have long legs, opt for the larger size. If you are growing and are near the top of a size range, you may want to go for the next larger size.