Calculate how much paint you need for your project. Enter your room dimensions, doors, and windows to get an accurate estimate in gallons for any number of coats.
Standard door ~21 sq ft
Standard window ~12 sq ft
Total Wall Area
352 sq ft
Doors & Windows
−45 sq ft
Paintable Area
307 sq ft
Paint Needed
1.8 gallons
at 350 sq ft/gallon × 2 coats
Estimated costs at different price points per gallon
Budget
$25/gallon
$45.00
1.8 gallons
Standard
$35/gallon
$63.00
1.8 gallons
Premium
$50/gallon
$90.00
1.8 gallons
Percentage of total area covered by each coat
307 sq ft covered
307 sq ft covered
Visual representation of gallons and quarts required
4 quarts = 3.20 quarts
The calculator finds the total wall area by multiplying the room perimeter (2 × length + 2 × width) by the ceiling height. It then subtracts standard openings — about 21 square feet per door and 12 square feet per window — to get the paintable surface area. That area is multiplied by the number of coats and divided by 350 square feet per gallon, a conservative coverage estimate for interior latex paint on smooth walls. Textured surfaces, porous materials, or extreme color changes may need additional paint beyond this estimate.
One gallon of interior paint typically covers about 350–400 square feet on smooth surfaces. Rough or textured walls, bare drywall, and dark-to-light color changes may require more paint. This calculator uses 350 sq ft per gallon as a conservative estimate.
Two coats are recommended for most projects. A single coat may be sufficient if you're painting the same color over an existing coat in good condition. Use two coats when changing colors, painting over a darker shade, or applying paint to new drywall (after primer).
Yes — it's smart to buy about 10–15% more than calculated to account for touch-ups, uneven surfaces, and waste. Leftover paint is also useful for patching scuffs and nicks after moving in furniture.
Primer is recommended for new drywall, stained surfaces, or drastic color changes (e.g., dark to light). Many modern paints include primer (paint-and-primer-in-one), which works well for routine repainting over previously painted walls.
For L-shaped or irregular rooms, break the space into rectangular sections, measure each section's walls separately, and add the wall areas together. You can run this calculator once per section and sum the gallons needed.
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