Your
oil pan was originally designed for a specific
oil capacity. Your
oil pan manufacturer can tell you what that number is because they determined it. You need to know it.
Although Patrick's approach, leveling the pan, provides interesting additional information, it is a virtual certainty you will not take the time to level your vehicle or pan the next time you check your oil level, soooo ...
Drain the oil from your pan. Put it into quart-capacity containers. With the knowledge of how much oil your pan manufacturer built the pan to manage, begin filling the pan with the good used oil you just drained out. If it is less than the manufacturer's recommendation for his pan design, continue to fill until you have added the pan manufacturer's design volume for your pan.
Put the dipstick in, pull it out, and read the oil mark on the dipstick. No matter what Ford stamped on the dipstick, the oil mark you see is the oil pan manufacturer's design capacity target for that particular pan. Mark your dipstick as full at that level. When it reads low, add oil. When it does not, do not.
It is that simple and you will not need the leveling procedure — although it can add interesting additional information.