Paint Quantity Calculator
Total Wall Area (sq ft)
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Paintable Area (sq ft)
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Gallons Needed
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Gallons to Buy
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How to Calculate Paint Quantities
Total wall area = 2 × (length + width) × height. Subtract openings: standard doors are about 21 sq ft (3' × 7') and windows about 15 sq ft (3' × 5'). Multiply the paintable area by the number of coats to get total coverage needed.
One gallon of paint covers approximately 350 square feet per coat on smooth walls. Rough or textured surfaces may reduce coverage to 250-300 sq ft. Darker colors covering lighter ones (or vice versa) may need an extra coat or primer.
Always buy slightly more than calculated — 10% extra accounts for waste, touch-ups, and application method (rollers are more efficient than brushes). Keep leftover paint sealed tightly for future touch-ups. Latex paint lasts 2-10 years when stored properly.
Frequently Asked Questions
How much area does one gallon of paint cover?
Approximately 350 sq ft per coat on smooth surfaces. Rough/textured surfaces may only get 250-300 sq ft per gallon.
How many coats of paint do I need?
Two coats is standard for full coverage and durability. One coat may work for touch-ups or same-color refreshes. Three coats for dramatic color changes.
Should I subtract doors and windows?
Yes. Standard doors (21 sq ft) and windows (15 sq ft) should be subtracted from wall area to avoid buying excess paint.
How much extra paint should I buy?
Buy 10% extra for waste, spills, and future touch-ups. Round up to the nearest gallon. Leftover paint stores well in sealed containers.