Paint calculator
Enter the room size, openings, coats and the coverage printed on your paint. Two coats on the walls of a 12 × 12 ft room with 8 ft walls, one door and one window take about 2 gallons at 350 sq ft per gallon.
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How the calculator works
Paint area is the wall area (perimeter × height) minus doors and windows, plus the ceiling if you choose. Multiply by the number of coats and divide by the coverage per gallon.
Use the coverage on your can
Coverage depends on the product and the surface. Behr, for example, lists its Premium Plus interior paint at 250–400 sq ft per gallon and its Marquee interior paint at up to 400 sq ft per gallon (Behr). Rough, porous or new drywall soaks up more paint, so use the low end of the range there, and plan on primer for bare drywall or big color changes.
Gallons and quarts
Paint is sold in gallons (about 3.79 litres) and quarts (a quarter gallon). The calculator rounds up to whole gallons plus quarts so you are not caught short; a little leftover is useful for touch-ups.