The industry averages are 350 square feet per gallon for paint and 200 square feet per gallon for primer. The type of paint, the surface and the application method affect the final amount that a gallon covers. Using a brush or roller is the most efficient way to apply paint.
If a painter is painting over a dark color, or if he must make several patches, he should apply more than one coat. Some surfaces absorb more paint than others; in such a case, a painter should use a thicker coat or apply several coats. Most paint brands post information about the coverage of their products on their websites.