BCBetter Calculators

Paint Calculator

Calculate how many gallons of paint you need to cover a room.

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Enter your values and click Calculate

How It Works

Wall area is calculated as: 2 × (length + width) × height. This gives the total area of all four walls. Door area (21 sq ft per door) and window area (15 sq ft per window) are subtracted to get the paintable area. Gallons needed = paintable area × number of coats ÷ 350, rounded up to the nearest whole gallon. The 350 sq ft per gallon coverage is a standard industry estimate for interior latex paint on smooth, primed drywall. Textured, rough, or unprimed walls absorb more paint — use 300 sq ft per gallon as a conservative estimate in those cases. The 21 sq ft door figure assumes a standard 3×7 ft door. The 15 sq ft window figure assumes an average double-hung window. Actual door and window sizes vary, so adjust your purchase if yours are significantly larger.

Examples

Standard Bedroom
12×10 ft room, 8 ft ceiling, 1 door, 2 windows, 2 coats.
Result: Paintable area ≈ 315 sq ft. About 2 gallons needed for 2 coats.
Large Living Room
20×16 ft room, 9 ft ceiling, 2 doors, 4 windows, 2 coats.
Result: Paintable area ≈ 636 sq ft. About 4 gallons needed.
Single Accent Wall
Painting one 14 ft wide wall, 8 ft tall, no doors or windows, 1 coat.
Result: Paintable area = 120 sq ft (the two 14 ft walls + two 1 ft walls × 8 ft). About 1 gallon.

Frequently Asked Questions

How many square feet does a gallon of paint cover?
Most interior latex paints cover 350–400 square feet per gallon on smooth, primed surfaces. This calculator uses 350 sq ft as a conservative standard. High-build primers and specialty paints may cover less — always check the label. On raw, porous, or heavily textured surfaces, coverage can drop to 200–300 sq ft per gallon. When in doubt, round up — having leftover paint for touch-ups is far better than running out mid-wall.
Do I really need two coats?
For most paint jobs — especially color changes, covering a dark color with a lighter one, or painting over bare drywall — two coats are necessary to achieve full coverage and color accuracy. A single coat often looks uneven or shows the previous color bleeding through. If you are repainting with the same or a similar color on a well-primed surface, one coat may suffice. Premium paints marketed as 'one-coat' can sometimes achieve full coverage in a single application on previously painted surfaces.
Should I paint the ceiling with the same paint?
No — ceiling paint is formulated separately from wall paint. It is thicker, has a flat sheen that hides imperfections, and is designed to prevent drips during application. Ceiling paint is typically white or light in color. This calculator only estimates wall paint. For the ceiling, calculate separately: ceiling area = room length × room width, and divide by 350 for gallons. Trim, baseboards, and doors require additional paint — usually 1 quart of semi-gloss or gloss trim paint per room.
What type of paint finish should I use?
Flat or matte finishes hide imperfections well and are good for ceilings and low-traffic rooms. Eggshell is the most popular wall finish — it has a slight sheen, is washable, and works well in living rooms and bedrooms. Satin is more durable and easy to clean, making it suitable for hallways, kitchens, and children's rooms. Semi-gloss and gloss finishes are very durable and moisture-resistant, ideal for trim, doors, kitchens, and bathrooms. Higher sheen = more durable but shows surface imperfections more clearly.

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