01-21-2014 06:56 PM
Whether interior or exterior, the "ball park" figure is about 300 square feet per gallon. There are many factors which can affect the coverage of paint; how much texture on the surface, how dry the substrate is, how significant a color change etc. Some of these variants might make it desireable to use a dedicated primer or two coats of one of the "paint and primer in one" products, such as the Behr Ultra line, both interior and exterior.
I encourage the use of the 8 ounce sample jars, not just for a real world audition of the color, but whether it appears that one coat will be adequate for the color change. Under ideal circumstances, one coat may be perfectly suited. However, it is never wrong to prime, although at times it is overkill.
To answer your question directly: it appears you will need somewhere around 6 or 7 gallons. That is, one 5 gallon bucket and one or two single gallons.
Hope this has helped.