Paint Calculator
Room Dimensions
Subtract Openings
Options
Gallons Needed
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Area to Paint
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Based on 350 sq ft coverage per gallon. Rounded up to the nearest quart.
What is a Paint Calculator?
A paint calculator estimates how many gallons of paint you need to cover the walls (and optionally ceiling) of a room. It takes your room dimensions, subtracts area for doors and windows, multiplies by the number of coats, and divides by typical paint coverage to give you a reliable quantity before your next hardware store trip.
How It Works
350 sq ft per gallon is the standard coverage for most interior latex paints on a smooth, primed surface. Rough or unpainted surfaces may need more.
Example
A bedroom that is 12 ft × 10 ft with 8 ft ceilings, 1 door, and 2 windows, with 2 coats:
- Wall area = 2 × (12 + 10) × 8 = 352 sq ft
- Subtract 1 door + 2 windows = 21 + 30 = −51 sq ft
- Net area = 301 sq ft × 2 coats = 602 sq ft
- Gallons needed = 602 / 350 = 2 gallons (rounded up)
Tips
- Always buy slightly more than calculated — a quart extra is cheap insurance against touch-ups later.
- Dark or saturated colors often need 3 coats over white primer, especially red and yellow hues.
- Textured surfaces (orange peel, knockdown) can absorb 20–30% more paint. Consider rounding up a full gallon.
- Flat/matte finishes hide imperfections better; semi-gloss and gloss are easier to clean but show flaws more.
- One gallon of primer is usually sufficient for most standard rooms before top coat.
Frequently Asked Questions
How much does a gallon of paint cover?
Most interior latex paints cover 350–400 sq ft per gallon on a smooth, primed surface. This calculator uses 350 sq ft for a slightly conservative estimate. Premium paints with higher solid content may cover more; cheaper paints and rough surfaces may cover less.
Do I need to prime first?
Yes, in most cases. Primer is especially important when painting bare drywall, going from a dark to light color, or painting over stains. Primer is calculated separately — run the calculator again with 1 coat to estimate primer coverage.
Should I paint the ceiling the same color as the walls?
Not necessarily. A white or slightly lighter ceiling is a classic choice that makes rooms feel taller. Matching the wall color is a bold look that can feel cozy. Toggle "Paint ceiling" to see how much extra paint that requires.
How long does a gallon of paint last in storage?
Properly sealed latex paint lasts 2–10 years in storage. Store it upside down to create an airtight seal with dried paint along the rim. Keep it at room temperature — freezing ruins latex paint permanently.