1/TPI = vertical distance traveled (inches) in one turn. Always round that number up, so you seat too shallow. It’s easier to add more turns than to pull the bullet and start over.
Standard dies are 7/8-14 = 1/14″ per turn 0.01″ per 1/8 turn is a healthy over-estimate.
Lee seater stems: use +0.015″ per 1/4 turn to estimate. Actual number is 18TPI and closer to 0.1388…89″.