Paint Calculator — Free Gallons & Cost Estimator

A 12 × 14 ft room with 8 ft ceilings, 1 door, and 2 windows needs approximately 3 gallons of eggshell paint for 2 coats. The math: 2 × (12 + 14) × 8 = 416 sq ft of walls; subtract 21 (door) + 30 (windows) = 365 sq ft; 365 × 2 coats = 730 total sq ft; 730 ÷ 350 sq ft/gal = 2.09 gal → round up to 3 gallons. For a single coat or flat finish, 2 gallons may suffice.

One gallon of paint covers approximately 250–400 square feet per coat, depending on the sheen. Flat and matte finishes spread farthest (~400 sq ft/gal) because they have more fillers. High-gloss finishes have more resin and cover less area (~250 sq ft/gal) but are harder and more washable. For eggshell and satin — the most common interior finishes — plan on 350 sq ft per gallon per coat.

Buy quarts when you need less than 1 gallon. One quart = 0.25 gallons and covers about 75–100 sq ft per coat. Quarts are ideal for accent walls, touch-ups, small bathrooms, or testing a color before committing. Per-ounce, quarts cost about 40–60% more than gallons — so if you need more than a quart, buying a gallon is almost always the better value. Most interior rooms need at least 1–2 gallons, making quarts uneconomical for full rooms.

For vaulted or cathedral ceilings, calculate the actual slanted wall area instead of assuming a flat rectangle. For a simple triangular vault: additional area = 0.5 × room length × vault height above standard ceiling. Example: 14 ft room with a 3 ft vault peak adds 0.5 × 14 × 3 = 21 sq ft per triangular wall end. Use the Custom Area tab above to enter your measured total manually for unusual room shapes.

Paint-and-primer-in-one products are thicker paints with better hiding power — they work well when repainting a similar color over a clean, intact existing finish. They are not a substitute for true primer on new drywall, heavily stained surfaces, or dramatic color changes. For those situations, use a dedicated primer coat (PVA for new drywall, shellac or oil-based for stains), followed by two coats of finish paint. Skipping primer on new drywall causes "flashing" — uneven sheen where tape joints absorb paint differently than skim coat.

Professional painters typically charge $300–$800 per room for a standard 12 × 14 ft bedroom (two coats, walls only, no ceiling). A full interior paint job for a 2,000 sq ft house — including walls, ceilings, and trim — usually runs $3,000–$8,000. Factors affecting price: ceiling height (above 9 ft adds cost), number of colors, condition of existing walls (heavy prep adds $0.50–$2/sq ft), and your geographic market.

Most latex paints are touch-dry in 1–2 hours and ready for a second coat in 4 hours at 70°F and 50% relative humidity. Oil-based paints take 6–8 hours between coats. Never rush the recoat window — applying a second coat before the first is fully cured causes wrinkling, peeling, and poor adhesion. In cold or humid conditions, add 2–4 extra hours to the manufacturer's stated recoat time.

Yes, almost always. Switching from a dark color (navy, black, deep red) to a lighter color requires primer — without it, you'll need 3–4 coats of finish paint instead of 2. Tinted primer matching your top coat color is the professional standard: gray primer under light colors, tinted gray or beige under dark colors. Primers also seal new drywall (which absorbs paint unevenly), cover stains, and improve adhesion on slick surfaces like glossy trim or previously painted cabinets. Budget $30–$50 for a quality primer gallon; it saves you $100–$200 in extra finish coats.