Paint Calculator
Enter your room's wall perimeter and height — we subtract doors and windows and multiply by coats to get the gallons to buy.
Perimeter = walk the walls and add their lengths. A 12×12 room has a 48 ft perimeter; a 10×14 room, 48 ft too.
How the math works
paintable area = wall area − (doors × 21 sq ft) − (windows × 12 sq ft)
gallons = paintable area × coats ÷ 350
One gallon of interior paint covers about 350 square feet per coat on smooth walls. We subtract a standard interior door at 21 sq ft (3' × 7') and an average window at 12 sq ft. If your walls are heavily textured, freshly patched bare drywall, or you're making a drastic dark-to-light color change, coverage drops closer to 300 sq ft per gallon — buy accordingly.
One coat or two?
Two coats is the default for a reason: it's what gives even color and scrubability. Repainting the same or a very similar color can sometimes be one coat. New drywall needs a primer coat plus two finish coats — count the primer as one of the three.
FAQ
- Should the ceiling be included?
- This calculator covers walls only. For ceilings, add ceiling area (length × width) ÷ 350 × coats of ceiling paint.
- How much trim paint do I need?
- Baseboards and casings typically take 1 quart per 300 linear feet per coat — usually one quart per average room is plenty.
- Does expensive paint cover better?
- Higher-quality paints contain more solids and often cover in fewer coats, which can make them cheaper per project.