The steps per is a calculation that takes into consideration all the components that you use for the axis. The link below brings you to a user support forum thread with an attachment spreadsheet to help you determine your steps per unit. You can also read the Mach3 Manual (link below) starting on page 73 in the pdf for more information. We also have a support video on using the Steps Per Unit Calculator Wizard in Mach4 (link below). 

https://www.machsupport.com/forum/index.php?topic=16315.0

https://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_Install_Config.pdf

https://youtu.be/d-xCWDR0Uvg