Paint Calculator
Calculate how much paint you need for any room. Accounts for doors, windows, and number of coats to give you an accurate gallon count and cost estimate.
Quick Answer
One gallon of paint covers approximately 350 sq ft per coat. For a standard 12x10 room with 8-foot ceilings (1 door, 2 windows, 2 coats), you need about 2 gallons. Formula: paintable area = total wall area minus doors (21 sq ft each) minus windows (12 sq ft each), then divide by 350 per coat.
2 coats recommended for most projects. Use 1 coat for touch-ups or same-color refreshes.
Paint Estimate
Cost Estimate
About This Tool
Estimating paint quantities correctly saves both money and trips to the hardware store. Buy too little and you risk color mismatches between batches. Buy too much and you waste money on paint that may dry out before your next project. This calculator uses the industry-standard coverage rate of 350 square feet per gallon to give you a reliable estimate.
How the Calculation Works
The calculator measures the perimeter of the room (2 x length + 2 x width) and multiplies by ceiling height to get total wall area. It then subtracts standard door openings (21 sq ft each for a standard 3' x 7' door) and windows (12 sq ft each for a standard 3' x 4' window). The remaining paintable area is multiplied by the number of coats and divided by 350 sq ft per gallon.
When to Use 1 vs 2 Coats
One coat is sufficient for: repainting with the same color, using paint-and-primer-in-one over a primed surface, or touch-up work. Two coats are recommended when: changing colors (especially going lighter over dark), painting new drywall (even if primed), using flat or matte finishes, or covering stains and patches. Three coats may be needed when painting over very dark colors with a light shade, or when using bright reds, oranges, or yellows which have lower opacity.
Tips for Buying Paint
Always buy all the paint you need at once and have the store mix it in one batch for color consistency. If you need multiple gallons, ask the store to "box" them (pour all gallons together and re-distribute) for uniform color. Keep leftover paint for touch-ups. Store it in a cool, dry place with the lid sealed tightly; properly stored latex paint lasts up to 10 years.
Coverage Variables
The 350 sq ft per gallon figure assumes a smooth, primed surface with a roller application. Rough or textured surfaces may reduce coverage by 10-25%. Spraying can increase coverage but wastes more paint through overspray. Dark base paints may cover as little as 250 sq ft per gallon. High-quality paints generally provide better coverage than budget options.
Frequently Asked Questions
How much does one gallon of paint actually cover?
Do I need primer before painting?
How do I account for textured walls or ceilings?
How long should I wait between coats?
Should I paint the ceiling too?
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