To work this out, you'd need to know the pitch of your leadscrews...and if your stepper driver board is using microstepping - do you know?

If you don't know but have access to a dial meter (pretty essential if you've a CNC machine), then goto to the mach 3 settings 'tab' (ie one of the other screens) & click on calibrate axis (that's from memory...so might be just calibrate) - choose an axis ....instruct mach3 to move your axis say 5mm is the 'distance to move' box (again from memory)!) - then see how far it actually moves by looking at the dial meter - tell mach3 this info (it'll ask you after it has moved the axis "how far did the axis move?") & it'll auto alculate your steps per unit for you.