Paint Calculator
Work out exactly how many gallons of paint your room needs, accounting for wall area, number of coats, and door/window deductions.
*Estimates only. Actual coverage varies by paint brand, wall texture, and color change. Cost assumes ~$35/gallon.
🎨 Planning Your Paint Job
How to measure a room accurately and avoid buying too much or too little paint.
How it Works
Multiplies wall width by height and number of walls to get total area, subtracts door and window space, then divides by your paint's coverage rate and multiplies by number of coats.
The Formula
Gallons = ((Wall Area − Door/Window Area) x Coats) / Coverage per Gallon. Doors deduct ~21 sq ft each, windows ~15 sq ft each.
Pro Tip
Buy an extra quart beyond your calculated total for future touch-ups — paint from the same can and batch matches sheen and color far better than a new purchase months later.
Frequently Asked Questions
How many gallons of paint do I need for a room? +
Divide your total wall area in square feet by the paint's coverage rate (usually about 350 sq ft per gallon), then multiply by the number of coats you plan to apply. Subtract the area of doors and windows first since those don't need paint.
How many coats of paint do I need? +
Two coats is standard for most repaints, especially when changing colors or covering a darker shade. A single coat may be enough for touch-ups or repainting the exact same color. Dramatic color changes (light to dark or vice versa) sometimes need a tinted primer plus two coats.
Does paint coverage vary by paint type? +
Yes. Most standard latex wall paints cover 350-400 sq ft per gallon on smooth surfaces, but textured walls, unprimed drywall, and darker colors can reduce effective coverage to 250-300 sq ft per gallon. Always check the coverage stated on your specific paint can.
Should I round up when buying paint? +
Yes, always round up to the next full gallon or quart, and consider buying slightly extra for touch-ups later. Running out mid-project and needing a can from a different batch can cause a visible color/sheen mismatch.
Do I need to paint the ceiling separately? +
Yes, ceilings are typically calculated separately using floor area (length x width) rather than wall area, and often use a flat ceiling paint rather than wall paint. This calculator estimates wall paint only.
How much paint do I need per square foot of wall? +
With standard 350 sq ft/gallon coverage, one gallon covers about 350 sq ft with a single coat, meaning roughly 0.0029 gallons per square foot per coat, or about a third of a fluid ounce per square foot per coat.