Pick a manufacturer...look at their website. It will show the cone of light from various fixtures. You may have to interpolate because your ceiling height is not standard. If you remember some trig, once you have the angle of coverage, you can figure it out for yourself. Each fixture is a little different and will cover a different area. Mood lighting is one thing, craft work and reading require different amounts of light. The angles may be wrong, so placement of both the lights and furniture can be critical. If instead of the big box store, you go to a real lighting store, you can have them help, or look through their catalogs to see what is available. There are so many manufacturers out there, and they all are a little different, there is no one pat answer...tie that into your specific needs and desires, and there are countless possibilities. It may be that the best solution is a combination of recessed, stand alone, and track lights. Maybe indirect with some sofits. Without knowing what you're trying to do, it's a crap shoot.