How Much Paint Do I Need?
It depends on room size and coat count, but one gallon of interior paint covers roughly 350-400 square feet with a single coat. For a 12x12 room with 8-foot ceilings, the walls total 384 square feet; subtract about 20 square feet for a door and 15 per window and you're near 334 square feet — roughly 1.7 gallons for the standard two coats, so buy two gallons. Our free paint calculator runs the math for any room instantly, or use the perimeter-times-height formula below to estimate by hand before you head to the store.
Key Takeaways
- Start with wall area: perimeter times ceiling height.
- Ceilings count separately from walls: a 12x12 ceiling is 144 square feet, so one gallon of ceiling paint covers two coats with room to spare.
- Trim, doors, and baseboards need their own estimate — one quart of trim paint covers roughly 100 square feet.
Explanation
Start with wall area: perimeter times ceiling height. A 14x16 living room has a 60-foot perimeter; with 8-foot ceilings that's 480 square feet of wall. Subtract about 20 square feet per door and 15 per window, since openings don't get painted. Divide what's left by 350 — the conservative end of coverage — to get gallons per coat, then multiply by your number of coats and round up to the nearest quart or gallon.
Plan on two coats whenever you're changing color; a single coat almost always shows roller marks and uneven tone. Going from a dark wall to a light one is harder still — budget a coat of tinted primer or a third coat of finish paint. Sheen matters less for quantity than for looks, but glossier finishes highlight patchy coverage, so your satin versus semi-gloss choice affects how forgiving each coat appears.
Surface condition changes the math. Textured walls — orange peel, knockdown, or brick — absorb 10 to 20 percent more paint than smooth drywall, so add that margin to your total. New, unprimed drywall drinks up the first coat, and a dedicated primer (which covers 200-300 square feet per gallon) is cheaper than extra finish paint. If you're covering wallpaper, check whether painting over it is a good idea before buying anything.
Buy smart: a gallon typically costs $30-60, while four quarts of the same paint can run $60-80, so round up to full gallons for walls. Estimate ceilings and trim separately — see how much paint a full room takes when you're painting every surface. Keep at least a labeled quart of leftover wall color for touch-ups; matching a custom tint two years later rarely comes out exact.
Things to Know
- Ceilings count separately from walls: a 12x12 ceiling is 144 square feet, so one gallon of ceiling paint covers two coats with room to spare.
- Trim, doors, and baseboards need their own estimate — one quart of trim paint covers roughly 100 square feet.
- Rooms with 9- or 10-foot ceilings need 12-25% more wall paint than an 8-foot room; recalculate as shown in How Many Gallons of Paint for a Bedroom? rather than guessing.
- Paint sprayers lose 20-40% of paint to overspray, so buy extra if you plan to spray instead of roll.
- Never pour leftover paint down a drain — dry out small amounts or take cans to a household hazardous waste collection site per EPA guidance.