So far it's just been a quart at a time, but that would mean that it's a little lower each oil change. I even have a base gasket leak and haven't had low oil yet. I just try to please the sight glass without overfilling, really. Too much oil can be a problem for seals and the life of the engine so do avoid that. I figure if I run low for some reason, I'll open another quart and keep it around until I need the next quart for an oil change and just rotate the old oil like food, always having an opened jug. That said, I haven't needed to do that yet.
The filter on these doesn't really hold oil like your car or truck and such, and it's even reusable. I keep a spare so I can alternate but I just clean them with penetrating oil and a brush.
Oh and one more thing, make sure to open the bleed bolt for the oil in the head a little bit when you start it and check for oil flow. Making sure it's getting up there is a good habit.