Paint Calculator

Work out the wall area (room perimeter × height, minus doors and windows), multiply by the number of coats, and divide by the paint’s coverage. A 13 × 10 ft room with 8 ft ceilings has about 368 sq ft (34 m²) of wall; minus 32 sq ft (3 m²) of openings, at two coats and 350 sq ft/gal (9 m²/L) coverage, that is 672 ÷ 350 ≈ 1.9 gallons (7 L).

Most latex paints and sheens cover 300–450 sq ft per gallon (8–11 m²/L) per coat on a sealed, smooth surface — the can states the figure. Porous surfaces drink more: new plaster, bagged brick and textured finishes can drop coverage below 250 sq ft/gal (6 m²/L) on the first coat, which is why primers and plaster primers pay for themselves.

Two finish coats is the standard for a solid, even color. Add a primer or sealer coat on new plaster or bare surfaces, and budget a third coat when covering a dark color with a light one — or use a tinted undercoat to save a finish coat.

Yes — they add up fast. A standard door is about 17 sq ft (1.6 m²) and windows commonly 10–20 sq ft (1–2 m²) each. Add up the openings and enter the total; the calculator deducts it before working out gallons. Skip the deduction only if you want the slack as spare paint.

Always — and buy it in one go, checking the batch numbers match, because separate batches can differ slightly in shade. Keep the leftover can labelled for touch-ups; walls patched from the same batch blend in far better than a later color match.