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Room DimensionsStandard door = 21 sq ft deducted
Standard window = 15 sq ft deducted
Affiliate Disclosure: This calculator is free to use. Some product links are affiliate links. Product links and pricing are for the US market.
How This Calculator Works
- Coverage: One gallon of paint covers approximately 350 sq ft per coat on smooth surfaces. Textured walls reduce this to 250-300 sq ft. This calculator uses 350 sq ft as the standard.
- Doors and windows: Standard door = 21 sq ft. Standard window = 15 sq ft. These are deducted from the total wall area.
- Ceiling: Ceiling paint is calculated separately since it's typically a different product (flat white).
- Always round up. If the math says 2.3 gallons, buy 3. You'll need touch-up paint later, and partial gallons aren't sold. The leftover is never wasted.