Paintable wall area = perimeter × height minus doors (~21 ft² each) and windows (~15 ft² each). Gallons = area × coats ÷ coverage (default 350 ft²/gal), rounded up.
How many coats should I plan for?
Two coats is standard for walls. One coat may suffice over similar color; new color or bare drywall often needs two. Adjust the coats field in the calculator.
Does this include ceiling paint?
Add ceiling area per room in the optional ceiling field, or use our ceiling paint calculator variant for length × width ceilings.