Calculate how many gallons of paint you need for walls. Enter wall area, subtract windows and doors, set coverage rate and coats for accurate estimates.
Painting walls is one of the simplest and most impactful home improvement projects you can undertake. Whether you're refreshing a single bedroom or repainting your entire house interior, knowing exactly how much paint to buy is crucial. Buying too little means an extra trip to the store and potential color-matching issues between batches. Buying too much wastes money on paint that may dry out before you ever use it.
This wall paint coverage calculator helps you determine the precise number of gallons needed for your project. Simply enter your total wall area, subtract the area of windows and doors, choose your paint's coverage rate, and select the number of coats. The calculator accounts for real-world coverage factors to give you an accurate paint quantity estimate.
Professional painters and DIY homeowners alike rely on accurate material estimates to plan budgets, avoid delays, and ensure color consistency across all walls. Use this tool before every painting project to order confidently.
Paint is sold by the gallon, and coverage rates vary significantly by paint quality, finish, and surface texture. A flat latex may cover 400 square feet per gallon on smooth drywall, while a semi-gloss on textured walls might only cover 250 square feet. This calculator lets you adjust for your specific situation so you buy the right amount the first time.
Paintable Area = Total Wall Area − Window Area − Door Area Gallons = (Paintable Area ÷ Coverage per Gallon) × Number of Coats
Result: 3.99 gallons
An 800 sq ft wall area minus 60 sq ft of windows and 42 sq ft of doors leaves 698 sq ft of paintable surface. At 350 sq ft per gallon coverage and 2 coats, you need 698 ÷ 350 × 2 = 3.99 gallons. Round up to 4 gallons for purchase.
Paint coverage is measured in square feet per gallon and depends on the paint's solid content, the surface texture, and the application method. Higher-quality paints with more solids (pigment and resin) generally cover more area per gallon and require fewer coats.
Surface porosity is the biggest variable. New, unprimed drywall absorbs paint and reduces coverage by 25–50%. Textured surfaces like knockdown or orange peel have more surface area per square foot, reducing effective coverage. Previously painted smooth walls provide the best coverage rates.
For rectangular rooms, add all four wall lengths together. For L-shaped or irregular rooms, measure each wall segment individually. Multiply the total perimeter by ceiling height to get gross wall area, then subtract all window and door openings.
One coat is rarely sufficient for a professional-looking finish. Two coats builds uniform color depth and hides roller marks. Three coats may be needed for reds, yellows, and other low-hiding pigments, or when making dramatic color transitions.
Most interior latex paints cover 350–400 square feet per gallon on smooth, primed surfaces. Coverage drops to 250–300 sq ft on textured or porous surfaces. Always check the specific coverage rate listed on your paint can.
Yes. Standard doors are about 21 sq ft (3×7 ft) and average windows are about 12–15 sq ft. Subtracting these areas prevents you from buying excess paint and gives a more accurate estimate.
Two coats is standard for most interior painting projects. You may need 3 coats when covering dark colors with light paint, applying bold or red-based colors, or painting over unprimed new drywall.
Primer is recommended for new drywall, stained surfaces, and dramatic color changes. Many modern paints include paint-and-primer in one, but a dedicated primer often provides better adhesion and coverage on problematic surfaces.
Measure the room perimeter (sum of all wall lengths) and multiply by the ceiling height. For a 12×14 ft room with 8 ft ceilings: perimeter = 52 ft, wall area = 52 × 8 = 416 sq ft.
Yes, slightly. Flat and matte finishes generally cover a bit more area per gallon than semi-gloss and high-gloss finishes. The difference is usually 10–15%, but check the can label for the exact specification.
Keep at least a quart (0.25 gallon) extra for future touch-ups. Store it in a cool, dry place with the lid sealed tightly. Properly stored latex paint can last 5–10 years.
Most home improvement stores accept returns of unopened, unmixed paint within 30–90 days. Custom-tinted paint is usually non-returnable, so accurate calculation before purchase is especially important for custom colors.