Calculating How Much Paint You Need for a Project

Last updated July 2, 2026

Paint coverage calculations divide the total surface area to be painted by the coverage rate stated on the paint can, typically 350 to 400 square feet per gallon for a single coat on a properly primed surface, though this rate decreases for textured surfaces, porous materials, or when applying paint over a significantly different base color requiring additional coverage for adequate hide. A room with 400 square feet of wall area requiring two coats needs 800 total square feet of coverage, which at 375 square feet per gallon requires approximately 2.1 gallons, typically rounded up to 2.5 or 3 gallons to ensure adequate supply without running short mid-project.

Door and window openings should be subtracted from the gross wall area calculation, since painting around these openings does not require covering the openings themselves, though many painters calculate a small buffer rather than precisely subtracting every opening, since the time saved on precise measurement often does not justify the marginal paint cost difference for typical residential rooms. Darker or more saturated paint colors frequently require an additional coat compared to lighter colors to achieve adequate coverage and color consistency, a factor that should be incorporated into the coat count used in the coverage calculation rather than assumed to be a uniform two-coat requirement regardless of color choice.

The calculation shows paint needed using the manufacturer's stated coverage rate divided into your total square footage requiring coverage, multiplied by your expected number of coats, which may need to increase for darker colors or significant color changes. Round up to the nearest convenient purchase quantity rather than buying the precise calculated amount, since running short mid-project creates color matching challenges if additional paint must be purchased from a different production batch.