Most adults choose a 20" unicycle to learn on, although a 24" may be better in some instances:

• 20" is preferred by people who like to do tricks, eg. BMX riders, Skate boarders and Jugglers. It is better ridden on smooth flat ground.
• 24" is preferred by riders who like to move. eg. Mountain bikers and road cyclists. This can be used on rougher ground than the 20" and needs more space to learn in.