Paint planning starts with surface area and ends with product coverage. Doors, windows, texture, primer, color changes, and the number of coats can materially change the quantity.
Calculate paintable area
For a rectangular room, perimeter × wall height gives wall area. Subtract doors and windows when their area is meaningful. Add ceilings or trim separately if they use different products.
Apply coats and coverage
If the paintable area is 500 square feet, two coats require 1,000 square feet of coverage. At a product coverage of 350 square feet per gallon, the result is 1,000 ÷ 350 = 2.86 gallons, so buy 3 gallons before practical allowances.
Why the label wins
Coverage depends on surface porosity, texture, application method, color, and the product itself. A rough or unprimed wall may consume more than a smooth previously painted surface.
Avoid color and batch problems
Buy enough paint from the same batch when possible, keep the label, and mix cans together for large areas if the manufacturer permits. Protect ventilation and follow product safety instructions.
Sources
The figures and rules in this guide are checked against:
- How Much Paint Do I Need? Paint Calculator — PPG Paints
- Paint Calculator — Benjamin Moore
- Paint Calculator — Dulux (AkzoNobel)
- Paint Calculator — Behr