By CalculatorInn Team · Updated: 2026-03-22 · Free & accurate · Instant results
Estimate how many gallons of paint you need based on room dimensions, number of coats, and window/door openings.
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Wall Area = 2 × (Length + Width) × Height; Paintable = Wall Area − Doors − Windows; Gallons = (Paintable × Coats) / 350
One gallon of paint covers approximately 350 square feet. Standard doors are ~21 sq ft and windows ~15 sq ft. Subtract these from the total wall area before calculating paint needed.
One gallon covers approximately 350-400 square feet on smooth surfaces with one coat. Rough or textured surfaces may require more paint per square foot.
Almost always yes. Two coats provide better coverage, durability, and color depth. Going from a dark to light color may even need 3 coats or a primer first.
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