Paint Coverage Area Calculator
Paint quantity is the paintable area times the number of coats, divided by the spread rate of your paint. The paintable area is the wall area minus doors and windows. Spread rate is the square feet a gallon covers in one coat and is printed on the can, varying with product, texture, and color change, so it is a user input here. This calculator subtracts your openings, multiplies by coats, divides by your spread rate, and rounds up to whole gallons so you do not run short mid-wall.
Paint coverage formula
Paintable area = wall area - openings area
Total area = paintable area * coats
Gallons (exact) = total area / spread rate
Gallons to buy = ceil(gallons exact)
Spread rate comes from the paint can and reflects your product and surface. Rough or porous walls and large color changes reduce effective coverage and may need an extra coat. The final figure is rounded up to whole gallons.
Painting context
- A gallon commonly covers around 350 to 400 square feet per coat on a smooth surface.
- Two coats is typical for an even, durable finish, especially over a color change.
- Rough, porous, or textured surfaces use more paint than smooth drywall.
- Deduct large doors and windows to avoid over-ordering on big walls.
- Primer is a separate job with its own spread rate and coat count.
Paint coverage: frequently asked questions
How much paint do I need?
Multiply the paintable area by the number of coats, then divide by the spread rate of your paint in square feet per gallon. Subtract the area of doors and windows first. A gallon commonly covers around 350 to 400 square feet per coat, but the exact figure is on the can, so enter your product's spread rate.
What is paint spread rate?
Spread rate (or coverage) is how many square feet one gallon covers in a single coat at the recommended film thickness. It is printed on the paint can and varies by product, surface texture, and color change. Rough or porous surfaces and big color changes lower the effective spread rate and may need an extra coat.
How many coats should I plan for?
Two coats is typical for a durable, even finish, especially over a color change or fresh primer. A repaint in a similar color over a sound surface may need only one. Enter the number of coats you plan; the calculator multiplies the area by coats before dividing by spread rate.
Should I subtract doors and windows?
Yes, for accuracy on large openings. This calculator subtracts the total opening area you enter from the wall area before computing paint. For small rooms some painters skip the deduction and treat the surplus as insurance, but deducting large windows and doors avoids significant over-ordering.
Does primer count separately?
Yes. Primer has its own spread rate and is applied before the finish coats, so estimate it as its own job using the primer can's coverage. Self-priming paints fold priming into the finish coats but may still need two coats over bare or patched surfaces.
Official sources
- U.S. Environmental Protection Agency: EPA (paint, coatings, and indoor air quality).
- U.S. National Institute of Standards and Technology: NIST Unit Conversion (area and volume units).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.