Paint Calculator: How Much Paint Do I Need?
A gallon covers roughly 350–400 sq ft per coat on smooth, primed drywall. Measure the room, take out doors and windows, pick coats, and see gallons, quarts and the cheapest way to buy them.
How this calculator works
- Wall area = perimeter × height, minus about 21 sq ft per door and 15 sq ft per window.
- Gallons = area × coats ÷ coverage per gallon. Ceilings get two coats; primer covers about 300 sq ft per gallon on new drywall.
- The cheapest mix of 5-gallon buckets, gallons and quarts is chosen from your prices.
Paint questions
How much paint do I need for a 12×12 room?
With 8 ft walls, one door and two windows, the walls are about 333 sq ft. Two coats at 350 sq ft per gallon needs 1.9 gallons, so buy 2 gallons.
Do I really need two coats?
Usually. Two coats give even color and sheen, especially with lighter or brighter colors. A same-color refresh on sound paint can get away with one.
Does primer replace a coat of paint?
Primer seals new drywall and patches and blocks stains, but it is not a finish coat. "Paint and primer in one" helps on painted walls; bare drywall still benefits from a dedicated primer.
How much paint for trim?
A quart covers the trim and doors in most bedrooms; a gallon of semi-gloss usually covers trim for a whole small house.