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Paint Calculator
How much paint do you need? Enter your room dimensions, number of doors and windows, and desired number of coats to get an accurate gallon estimate with a built-in waste buffer.
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How This Calculator Works
This calculator measures total wall area from room dimensions, subtracts standard door and window openings, multiplies by the number of coats, and divides by paint coverage (350 sq ft/gallon) with a 10% waste buffer.
Formula: Paintable Area = (2 × (Length + Width) × Height) – (Doors × 21 sq ft) – (Windows × 15 sq ft). Gallons = (Paintable Area × Coats ÷ 350) × 1.10.
Assumptions & Limitations
- • Standard door opening: 21 sq ft (3'×7').
- • Standard window opening: 15 sq ft (3'×5').
- • Coverage: 350 sq ft per gallon (varies by paint quality and surface texture).
- • 10% waste buffer included for touch-ups and irregular surfaces.
- • Cost estimate uses $35/gallon for mid-range interior paint.