How much paint do I need?
Most paint covers about 350 square feet per gallon per coat on smooth, primed walls (rough or porous surfaces need more). The math: wall area minus doors and windows, times coats, divided by coverage.
Rules of thumb
- Wall area = 2 × (length + width) × height. A 12×10 ft room with 8 ft ceilings has 352 sq ft of walls.
- Deduct ~20 sq ft per door and ~15 sq ft per window.
- Two coats is the standard for a durable, even finish; three if you're making a drastic color change.
- Ceilings need their own coat — a 12×10 ceiling is 120 sq ft, roughly a third of a gallon.
Buying tips
Paint is sold in gallons and quarts. If you need 1.3 gallons, buy 1 gallon + 2 quarts (not 2 gallons — unless you want the extra for touch-ups, which is honestly not a bad idea). Keep leftover paint labeled with the room and color; it's the cheapest insurance for future repairs. And remember: primer is a separate product — if you're painting bare drywall or covering stains, budget a primer coat too.