Paint Calculator

The paint calculator estimates gallons needed by multiplying your surface area by the number of coats, then dividing by the coverage rate. One gallon of standard latex paint covers 350–400 square feet on a smooth, previously painted surface. Rough or porous surfaces — bare drywall, concrete block, textured ceilings — absorb 30–50% more, so always check the coverage rate listed on your specific product's label rather than using a generic number.

For a typical room, measure each wall's height and width, add them together, then subtract around 20 sq ft per standard door and 15 sq ft per window. Most interior projects use two coats — one isn't enough for an even finish unless you're going white over white with a high-hiding paint. Covering a dark color with a light one almost always needs three coats. Primer counts as a coat when using a paint-and-primer product; otherwise add a separate primer coat on bare drywall, previously stained surfaces, or dramatic color changes.

A common mistake is buying the minimum calculated quantity. Paint batches vary slightly in color (called a dye lot), and if you run short mid-project, new cans may not match exactly. Order one extra quart beyond what the calculator shows, or round up to the nearest full gallon. For exteriors, add another 10% for lap marks, backrolling, and the extra absorption from raw wood and rough siding. Keep leftover paint sealed and labeled — it's invaluable for touch-ups and impossible to match exactly years later.