Extra Small: 2" Most often a good size for children and the very petite
Small: 2.25" Best choice for those who are petite with small hands
Medium: 2.5" The size I wear! The most common size in my experience.
Large: 2.75" A good size for larger hands or if you have trouble putting on bangles
Extra Large: 3" Often a good choice for people with severely limited flexibility in their hands (usually due to arthritis) or for those with larger hands.