How much paint do I need?
The amount of paint you need depends on the wall area, how many coats you are applying, and how much of the wall is taken up by doors and windows. The formula this calculator uses is:
Paint (gallons) = (Wall area − openings) × coats ÷ coverage per gallon
Wall area is the room perimeter multiplied by the wall height: 2 × (length + width) × height. We subtract roughly 21 sq ft for each standard door and 15 sq ft for each window, then divide by 350 — the square footage a typical gallon covers in one coat — and round up to the nearest gallon.
Paint coverage at a glance
| Surface | Approx. coverage per gallon |
|---|---|
| Smooth, primed drywall | 350–400 sq ft |
| Lightly textured walls | 300–350 sq ft |
| Rough or porous surfaces | 200–300 sq ft |
| Primer | 200–300 sq ft |
Tips for an accurate estimate
- Plan for two coats. Most colors need two coats for an even finish — and always two when going darker.
- Add primer for big changes. Bare drywall, patches, stains, and dramatic color changes all need a primer coat.
- Buy it all at once. Paint mixed in different batches can vary slightly in shade. Round up and buy together.
- Keep some for touch-ups. A little leftover paint is worth it for scuffs and nicks later.