You probably should have different steps/inch on Z than for X and Y. This is a number that is calculated based on the hardware, not something you “adjust”. If you need to adjust this, you have problems with losing steps, backlash, bit not being it’s nominal size, or some other mechanical issue (loose couplers,etc.).
You are always looking for steps/unit so determine how many steps in one rotation of the stepper divided by how far it moves in one rotation. For example, on my machine I am going to replace a 1605 ballscrew with a 1610 (16mm dia x 10mm per rotation). So for me (200 steps per rotation x 10 microsteps) / 10mm = 200 steps/mm. Actually for my machine I work in inches, so it’s 5080 steps/in, but the math is the same.