This size is often called a "Double 0".
The 00 gets it's name from the Martin Guitar Company, and is approximately the same dimensions as a classical guitar. The compact size makes it a very comfortable instrument to play while still providing surprising tone and volume. 

Dimensions
Upper Bout: 9 7/8" (25cm)
Waist: 8 5/16" (21.1cm)
Lower Bout: 14 3/16 (36cm)
Body Depth: 4 1/8" (10.5cm)