Interior Paint Calculator

How painters estimate paint

Paint quantity comes down to net area, coverage per gallon, and coats. Net area is the paintable surface after subtracting doors and windows. Coverage varies by product but 350 square feet per gallon per coat is a reliable default for smooth walls rolled with a nap roller. Two coats is the standard finish; one coat is only realistic when a tinted primer is combined with a high-hide finish and there is no color change.

When to buy buckets

Once total volume exceeds about five gallons, buy a five-gallon bucket instead of five one-gallon cans. It is cheaper per gallon, and, more importantly, all the paint is from one batch which prevents subtle color shifts between cans. Any remainder can go into single gallons for touch-ups.

Primer, sheens, and sprayed application

Primer earns its keep on bare drywall, over stains, and when covering a dark color with a lighter one. Higher sheen finishes highlight surface flaws, so choose satin or eggshell on walls that are not perfectly smooth. Sprayed application uses about 30 to 50 percent more paint than rolling because of overspray, so raise the waste factor for spray work.