Single Room Paint Calculator
Free single room paint calculator — walls, doors, windows, coats and waste in exact gallons.
Runs entirely in your browser — room sizes and coverage figures never leave this pageTry: Room length=12, Room width=12, Wall height=8, Number of doors=2, Number of windows=2, Coverage per gallon=350, Number of coats=2, Waste factor=15, Surface condition=smooth, Color change=none → 384 sq ft, -72 sq ft, 312 sq ft, 20, 6240 sq ft, 20.5 gal, 21 gallons
How to use
Enter the room length, width and wall height, then count doors and windows. The calculator subtracts openings, applies your coats and waste factor, and rounds up to the gallons to buy. Choose "New drywall" or a color change and it also estimates primer.
FAQ
How do I calculate how much paint I need for a room?
Add the length and width, multiply by 2 for the perimeter, then multiply by wall height for gross wall area. Subtract doors (21 sq ft each) and windows (15 sq ft each), then divide by your paint's coverage per gallon and multiply by coats.
Do I need primer before painting?
Primer is recommended on new drywall, bare wood, stained or glossy surfaces, and for dramatic color changes. On previously painted smooth walls, two top coats usually work without primer.
How many coats of paint do I need?
Two coats are standard for even coverage. Dark-to-light or light-to-dark color changes often need a third coat or a quality primer first.
What is the difference between latex and oil-based paint?
Latex (water-based) dries fast, cleans up with soap and water, and is the standard for walls and ceilings. Oil-based (alkyd) is tougher and better for trim, but needs mineral spirits to clean up and has stronger fumes.
Why should I buy extra paint?
Buying about 10% extra covers touch-ups, mistakes, and coverage variations between brands. Running out mid-project means color-matching problems.