Drum Sticks are mostly given a number and a letter.
Usual sizes are for instance. 2a, 5a, 7a. There is no accurate standard to this system. The appropriate sizes vary from manufacturer to manufacturer.
General rule: Number 7 is a finer stick than number 2 5b is thicker than 5a.
Here a rough scale:
Between them there is a multitude of models; the characteristics differ depending on the make.