Look for a ballistics calculator like Quickload or Winchester ballistics calculator. The latter is free in the app store. Also one online here: http://www.biggameinfo.com/index.aspx?page=/balcalc.ascx . Using the Win ballistics app, choosing a .308 win 150 grain power, null wind 60 degrees ambient and sight hight of 1.5 inches, the drop calculated at -53.5 inches. Remember there are many factors involved including round ballistics coeff, altitude, temperature, etc.