Paint Calculator
Gallons, quarts & cost per room
Enter room dimensions
Each ~20 sq ft
Each ~15 sq ft
Your results
Enter your project details to see results.
Formula & explanation
Wall area is the perimeter times ceiling height, minus typical door (20 sq ft) and window (15 sq ft) openings. Multiply by the number of coats and the waste factor, then divide by ~350 sq ft per gallon of quality paint. Porous or dark surfaces may need more.
Example calculation
12 × 15 ft room, 8 ft walls, 2 doors, 2 windows, 2 coats, 10% waste, no ceiling:
Walls = 2×27×8 = 432 sq ft − (40+30) = 362 sq ft × 2 coats = 724 sq ft × 1.10 = 796 sq ft ÷ 350 = 2.3 → 3 gallons.
Buying & project-planning tips
- Buy primer for new drywall or drastic color changes — it saves a coat of finish paint.
- Quality paint covers better and often needs fewer coats, saving money overall.
- Dark colors over light walls may need a gray-tinted primer and 3+ coats.
- Buy all paint from one batch (same lot number) to ensure color consistency across the room.
- Rolling uses more paint than brushing — budget about 350 sq ft/gal for rolling, 300 for spraying.
Frequently asked questions
How much does a gallon of paint cover?+
Quality interior paint covers roughly 350 sq ft per gallon per coat on smooth, primed walls. Porous or unpainted surfaces may cover 250–300 sq ft.
How many coats do I need?+
Two coats is standard for an even, durable finish. One coat may suffice for a repaint with the same color; three may be needed for light over dark.
Should I paint the ceiling?+
Ceilings need their own paint — typically a flat finish. Add the ceiling area to your calculation if you're painting it the same project.
Do I need primer?+
Yes for new drywall, repairs, or drastic color changes. Tinted primer close to your finish color reduces the number of finish coats needed.