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How the paint estimate works
This calculator first finds the gross wall area of the room — 2 × (length + width) × height — then subtracts the area of doors and windows to get the net paintable surface. It divides that by your chosen coverage rate and multiplies by the number of coats to reach total gallons.
Coverage rate is the biggest variable. A gallon of flat latex paint typically covers about 350–400 sq ft on smooth, primed walls. Rough or unprimed surfaces — bare drywall, fresh plaster, or heavily textured walls — can drop coverage to 250–300 sq ft per gallon, so always check the label on your can. We default to 350 sq ft per gallon per coat as a safe middle value.
Two coats are standard. One coat rarely gives even, hide-the-old-color results; most pros apply two coats (or a primer plus two top coats for a dramatic color change). The suggested purchase rounds your gallon total up to the nearest quart and expresses it as a gallon + quart combination (1 gallon = 4 quarts), because paint is sold in both 1-gallon and 1-quart cans.
Common paint coverage quick reference
- Flat / matte latex: ~350–400 sq ft/gal
- Eggshell / satin: ~300–350 sq ft/gal
- Semi-gloss / gloss: ~250–300 sq ft/gal
- Primer (drywall): ~200–300 sq ft/gal
Buying tips
Measure each wall's height and total perimeter rather than guessing, and don't forget to subtract large openings such as sliding doors or picture windows. If your walls are freshly patched or you're changing from a dark to a light color, budget for a primer coat in addition to your top coats. Buying one extra quart is cheap insurance against running out mid-wall — and leftover paint keeps for touch-ups later.
More material tools
- Flooring calculator — boxes of tile or flooring to buy.
- Wallpaper calculator — rolls of wallpaper you'll need.
- Curtain fabric calculator — fabric panels and yardage.