Bonsai can be classified into different groups by size. The size of bonsai is generally measured as the distance between the top of the soil and the apex of the bonsai tree. Below is the classification of bonsai of different sizes.
Keishi Bonsai (thumb size) – Up to 1 inch (2.5 cm) in height
Shito Bonsai (very small) – Up to 3 inch (7.5 cm) in height
Mame Bonsai (mini) – Up to 6 inch (15 cm) in height
Shohin Bonsai (small) – Up to 8 inch (20 cm) in height
Kifu Sho Bonsai (medium) – Up to 16 inch (40.5 cm) in height
Chu Bonsai (medium large) – Up to 24 (61 cm) inch in height
Dai Bonsai (large) – Up to 40 (101.5 cm) inch in height
These are some standard rules that become important and helpful in shows and competitions. Yet, often, these measures are not sharply outlined, and the exact height of the bonsai tree does not hold very strictly. For example, the majority of shohin bonsai at most bonsai shows are approximately 8 inches (20 cm) or less in height. Yet, an elegant, slim bonsai tree may easily override the limit in height but still be considered as a shohin. And this is same for mame bonsai.
Basically, the main “rule” is that we must be able to hold our shohin bonsai and mame bonsai in one hand, on our palm. They must express the beauty of a large aged tree in miniature.