You are missing an important number: The pitch of the gear rack OR the diameter of the pinion. The number of teeth have nothing to do with the ratios unless you know the number of teeth per inch (TPI) of the matching rack OR you know the diameter of the pinion. That is because the distance it moves per rev is a function of the circumference of that gear. The TPI of the rack and the number of teeth on the circumference lets you do the same math.
The formula for calculating the number of steps per inch with R & P are covered in the BladeRunner AIO User Manuel (3 parts) on the CandCNC website on the manuals page . Find the section on Table Physics to get an illustrated tutorial on that and motor tuning.