How the paint calculator works
We take your wall area (perimeter × height), subtract about 20 sq ft per door and 15 sq ft per window, multiply by the number of coats, then divide by 350 sq ft — the coverage of a typical gallon. Result is rounded up to whole gallons.
Tips for an accurate estimate
Fresh drywall and dark-to-light color changes drink more paint — plan on an extra coat. Primer counts as a coat. One gallon covers about 350 sq ft on smooth walls; rough or textured surfaces drop to ~300.
Should I paint the ceiling too?
Add ceiling area (length × width) to your wall total and use ceiling paint — it's flatter to hide roller lines. This calculator covers walls; add the ceiling separately if needed.