As Jester mentioned, it depends on brand and on the color itself. Some colors cover better than others and it's extremely difficult to say that 2 coats will cover the substrate completely. It also depends on the color of the substrate, the experience of the painter, a painter with a good deal of experience will know how to stretch a quart of paint to make it go further than an inexperienced painter.
So your doing the outside, door jambs...what about under the hood, under the trunk lid, interior dash, interior door frames, insides of fenders, engine bay, undercarriage? These are all things that need to be factored in before suggesting the amount of paint you need.
If you can give us more information we can give you a better estimate of the amount of paint you need.