I am setting up my cnc mill with mach 3 and have everything running great i just don't know how to figure out how many steps per  inch i need to be accurate. it is set to the default 4000 right now but that is way off far to phew steps for my machine. if anyone has any input please help.

You can look at the settings page, above the reset button, set steps per it will help.

    Here is how you do the math. I will give you mine as an example. What we need to know is, How many pulses from Mach will it take to move the machine 1 of your units? (inch,mm) Mine is in inches. 1 inch = 10,000 pulses on mine. This is how I came up with the number.
My steppers have 200 pulses per revolution. ( 360 degrees divided by 1.8 degrees = 200 )
Micro stepping = 10. So 200 X 10=2,000
Motor to screw gearing is 1-1. So 2,000 X 1=2,000
Screw lead is .200 of an inch. My screw will have to turn 5 rounds to move the nut 1". 1.0 divided by 0.200=5. So 2,000 X 5=10,000.

Brett

how do i know what mode my steppers are in?

Most steppers are 200 steps/rev, some are 400. If you try with 200 fist and your table moves exactly half of the distance its meant to then yours must be 400 steps so just double your steps/unit and it will be right.
 Hood

so the steppers come pre-set?

In a sense yes, but it is actually the way they are built that determines whether they are 200 or 400 steps per rev, it cant be changed.
Hood