Quick answer
The Paint Calculator shows gallons of paint for walls, minus doors and windows, for any number of coats. How it works: Wall area = perimeter × height; Paintable area = wall area − 21 sq ft per door − 15 sq ft per window. For example, with room perimeter of 48 ft, wall height of 8 ft, and doors of 1, the paint needed is 1.9 gallons.
How to use the Paint Calculator
- Enter room perimeter. Add up the length of every wall.
- Enter wall height.
- Enter doors.
- Enter windows.
- Enter coats.
- Open Assumptions and rates to change any rate or fee to match your account.
- Read paint needed and the breakdown. Use Share to send the exact numbers, or Print to save a PDF.
How it's calculated
- Wall area = perimeter × height
- Paintable area = wall area − 21 sq ft per door − 15 sq ft per window
- Gallons = paintable area × coats ÷ coverage
Worked example
With room perimeter of 48 ft, wall height of 8 ft, doors of 1, windows of 2, and coats of 2:
Paint needed: 1.9 gallons. Buy: 2 gallon cans.
Questions people ask
Do I need primer?
Use primer on new drywall, stains, or big color changes. Primer often covers less area per gallon.