Paint Calculator
Enter your wall dimensions, doors, and windows to see exactly how many gallons of paint you need — doors (21 ft²) and windows (12 ft²) are deducted automatically, and results round up to the quarter gallon.
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How much paint do I need?
Multiply each wall's length by its height and add them up, then subtract 21 ft² per door and 12 ft² per window — the standard deductions painters use. A gallon of quality paint covers about 350 ft² per coat on smooth, primed walls; rough or porous surfaces cover less, so drop the coverage number. Two coats is the norm for a color change, and buying to the quarter gallon avoids paying for a full extra can.