What Is the Paint Quantity Calculator?
This calculator estimates how many gallons of paint you need to cover your walls. By entering the total wall area, the number of coats you plan to apply, and how much area one gallon covers, you instantly get the paint quantity required — plus a rounded-up figure for how many cans to buy.
How to Use It
Measure your total wall area in square feet (multiply each wall's width by its height and add them together, subtracting large windows and doors if you wish). Enter the number of coats — two is typical for good coverage. Then enter the coverage rating of your paint, usually printed on the can. A standard gallon covers about 350 sq ft per coat.
The Formula Explained
The math is simple: $$\text{Gallons} = \left\lceil \frac{\text{Wall Area} \times \text{Coats}}{\text{Coverage per Gallon}} \right\rceil$$. Multiplying area by coats gives the total surface area you'll actually paint over. Dividing by the per-gallon coverage tells you how many gallons that takes. Because you can't buy a fraction of a can, we also round the result up to the next whole gallon.
Worked Example
Suppose your room has 400 sq ft of wall area and you want 2 coats. Your paint covers 350 sq ft per gallon. Total area painted = \(400 \times 2 = 800\) sq ft. $$\text{Gallons} = 800 \div 350 \approx 2.29 \text{ gallons}$$ You would buy 3 gallons to be safe.
FAQ
How many coats should I use? Two coats is standard. Use three when going from a dark to a light color or painting porous surfaces.
What coverage should I enter? Check your paint can — most interior latex paints cover 300–400 sq ft per gallon. Rough or unprimed surfaces cover less.
Should I subtract windows and doors? For a tighter estimate, subtract their area from your total. For a safety margin, leave them in.
