If your rotary is direct drive, i.e. the stepper motor is coupled directly to the roller or chuck, the steps per revolution of the stepper motor are the same as the steps per rotation of the rotary. It’s just the steps per revolution of the motor multiplied by the number micro-steps.
To calculate the steps per rotation of a belt driven rotary device,
S = steps per revolution of the stepper motor
u = # of micro-steps
MP = # of teeth on stepper motor pulley
RP = # of teeth on roller/chuck pulley
(S×u×RP)/MP=steps/rev
For example:
A standard NEMA 17 motor is typically 1.8° per step or 200 steps per revolution. Many of the stepper drivers are set up for 32 micro-steps. A common pulley size on the motor is 20 teeth and let’s say the roller pulley had 50 teeth. Plugging all the variables into the formula,
(200×32×50)/20=16000
so this hypothetical rotary is 16000 steps per revolution.