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Calculate how much paint you need for any room. Get gallons needed, coverage area, and cost estimates for walls and ceilings.
Estimating the right amount of paint prevents wasteful extra trips to the store and ensures you have enough to finish the job. Our paint calculator uses the standard method professional painters rely on: measure total wall area, subtract openings, multiply by the number of coats, and divide by per-gallon coverage.
Start by measuring your room length and width. Multiply the perimeter (2 x length + 2 x width) by your ceiling height to get total wall area. A standard 12x12 room with 8-foot ceilings has 384 sq ft of wall space. Subtract 21 sq ft per door (standard 3x7 ft) and 15 sq ft per window (standard 3x5 ft). The remaining area is what you need to paint.
Most interior latex paints cover 350-400 square feet per gallon on smooth, previously painted surfaces. Coverage drops on textured walls (250-300 sq ft), bare drywall (200-300 sq ft), and rough masonry (150-200 sq ft). Always check the label for the manufacturer's stated coverage rate.
Paint finish affects both appearance and durability. Flat finishes hide wall imperfections but are harder to clean, making them ideal for ceilings and low-traffic areas. Eggshell and satin provide a gentle sheen that wipes clean easily -- perfect for bedrooms, living rooms, and hallways. Semi-gloss and gloss stand up to moisture and scrubbing, which is why they are preferred for kitchens, bathrooms, trim, and doors.
Always buy all your paint at once to ensure consistent color (batch variations exist). Keep at least half a gallon extra for touch-ups. Stir paint thoroughly before use; never shake it, as shaking introduces bubbles. Use painter's tape for clean edges and remove it while the final coat is still slightly tacky for the crispest lines.
Big-box retailers like Home Depot and Lowe's offer volume discounts on 5-gallon buckets (typically 10-15% savings). Paint-and-primer-in-one products eliminate a separate priming step, saving time and money. Consider buying during holiday sales (Memorial Day, Labor Day, Black Friday) when paint is commonly discounted 25-40%.
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A 12x12 room with 8-foot ceilings has about 384 sq ft of wall space. After subtracting a door and two windows, you need about 1-2 gallons for two coats. One gallon covers approximately 350-400 sq ft.
Two coats is the standard recommendation for most projects. You may need three coats when painting over dark colors with light paint, or when using certain reds and yellows that have poor coverage.
Flat has no sheen and hides imperfections (best for ceilings). Eggshell has a slight sheen and is easy to clean (great for living rooms). Satin is durable and moisture-resistant (ideal for kitchens/baths). Semi-gloss and gloss are very durable (best for trim, doors, and cabinets).
One gallon of paint typically covers 350-400 square feet on smooth surfaces. Textured walls, bare drywall, or porous surfaces may require more paint. Always check the manufacturer's coverage rating on the can.
Primer is recommended when painting over bare drywall, dark colors, stains, or glossy surfaces. Many modern paints include primer (paint-and-primer-in-one), which works well for repainting similar colors on previously painted walls.
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