Work out how much paint to buy before you get to the store. Enter one or more rooms (or individual accent walls), the doors and windows to skip, how many coats, and the coverage from your paint label. The calculator returns the gallons for walls, ceiling, and trim separately — they are usually different paints — along with the primer and an optional cost estimate. Switch to metric to work in meters and liters.
Hanging new drywall first? The drywall calculator counts the sheets, mud, and tape, and the wallpaper calculator handles an accent wall in paper instead of paint. Still picking colors? Build a scheme with the color palette generator. Why one gallon per 400 square feet often under-orders, and where the waste goes, is worked through in how much paint, wallpaper, and tile to buy.
Frequently asked questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8 ft ceilings has 384 sq ft of wall (four 12 ft walls × 8 ft). Subtract one door (about 21 sq ft) and two windows (about 15 sq ft each) and you have roughly 333 sq ft to paint. At a typical 350–400 sq ft per gallon, one coat needs just under a gallon and two coats need about 1.8 gallons — so buy 2 gallons for the walls. The ceiling adds another 144 sq ft, which is under half a gallon per coat.
Why do I need two coats of paint?
One coat almost never hides the old color evenly, especially when going from dark to light or across patched areas. Paint also reaches its rated sheen, color depth, and washability only once a full film is built up. Coverage figures on the can are per coat, so the calculator multiplies the wall area by the number of coats. A third coat is common for deep reds, yellows, and other saturated colors, or you can use a gray-tinted primer first. Two thin coats also dry harder and more evenly than one heavy coat, which sags and shows roller marks.
How many square feet does a gallon of paint cover?
Most interior wall paints list 350–400 sq ft per gallon on the label for a smooth, previously painted surface; some premium lines claim up to 450. Real coverage is lower on textured walls, bare drywall, fresh joint compound, masonry, or when you roll thick. We default to 375 sq ft per gallon and let you edit it. If your walls are orange-peel or knockdown textured, try the low end of the range or lower. Rolling with a thicker-nap roller on rough surfaces also lays down more paint per square foot.
Should I subtract doors and windows?
Yes, for large openings it makes a real difference. The calculator subtracts 21 sq ft per door (a standard 3×7 ft door) and 15 sq ft per window (3×5 ft). A room with two doors and three windows loses close to 90 sq ft — about a quarter gallon per coat. If you have a picture window or a sliding glass door, add it as extra windows or reduce the wall width accordingly. Closets you are painting count as extra walls; closets you are skipping can be left out entirely.
Do I need primer?
Prime new drywall, big patches, stained areas, glossy surfaces, and dramatic color changes. Primer seals porous surfaces so the topcoat dries evenly and does not flash. Typical primer labels quote 300–400 sq ft per gallon; the calculator uses 300 because bare drywall is thirsty. On already-painted walls in good shape going to a similar color, a quality paint usually needs no separate primer. Oil-based or shellac primer is the fix for water stains, smoke, and knots in bare wood, which bleed through latex.
Should I buy gallons or quarts?
Quarts cost far more per ounce — often a third of the gallon price or more — so once you need three quarts, another gallon is usually the better buy. The calculator shows both options: whole gallons, and gallons plus quarts. Keep a little leftover from the same batch for touch-ups — paint mixed later can shift slightly in color. For large jobs, 5-gallon buckets are cheapest per gallon; box (mix) the cans together so the color is uniform. Write the color formula on the lid of your leftover can.