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Paint Gallon Estimator (With Window & Door Deductions)
Exactly how many gallons you need for any room — no waste, no shortage.
In this article
Standard paint coverage
One gallon of standard interior paint covers approximately 400 sq ft (one coat). Premium paints may cover 350–450 sq ft. Always deduct doors (~21 sq ft each) and windows (~15 sq ft each) for accuracy.
Buy slightly more than you need
Add 10% to your estimate for corners, roller waste, and touch-ups. Most stores allow returns of unopened gallons. Have leftover paint mixed: store it for 10 years for touch-ups — wall colors change more than you'd expect with patching and sunlight.
⚡ CalcWolf Insight
Premium paint at $50-70 per gallon often covers more per gallon than budget paint, making it effectively cheaper per finished square foot.
Frequently asked questions
How many gallons of paint do I need for a 12x12 room?▾
A 12×12 room with 9ft ceilings has ~396 sq ft of wall space (minus doors/windows ≈ 340 sq ft paintable). 2 coats = ~1.7 gallons. Buy 2 gallons for standard coverage.
How many coats of paint do I need?▾
Two coats is standard for most color changes. One coat works for touch-ups and same-color refreshes. Three coats are needed when going from dark to light colors or painting over stains. Self-priming paints reduce the number of coats by 1 compared to standard paint.
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