Use wall area directly or enter room dimensions. The result separates net surface area from the amount you should actually purchase.
01 / Formula
How this is calculated
Paint = ((wall area − doors − windows) × coats) ÷ coverage per gallon02 / Assumptions
What the estimate assumes
- ✓Coverage is per coat and can be edited to match the label on your paint.
- ✓A standard door is estimated at 20 sq ft and a standard window at 15 sq ft.
- ✓The purchase recommendation rounds up to common U.S. container sizes.
03 / Worked example
See the math in context
For 900 sq ft of walls, two doors, four windows, two coats, and 375 sq ft/gal coverage: net area is 800 sq ft, coated area is 1,600 sq ft, and the estimate is 4.27 gallons.
04 / Guidance
Measure first, buy second
For the best estimate, measure each wall separately and add the areas. Subtract only large openings; leaving small openings in the total often provides a useful buffer for touch-ups.
05 / Guidance
Use the product label
Texture, porosity, color change, paint quality, and application method affect real coverage. Replace the default coverage with the range stated by the manufacturer.
Questions
Frequently asked
Should I round up when buying paint?+
Yes. Paint is sold in fixed container sizes, and a small reserve helps with touch-ups, porous surfaces, and application loss. The calculator shows both the theoretical quantity and a practical purchase amount.
Does paint coverage include two coats?+
Coverage printed on a can is normally stated per coat. Two coats cover the same surface twice, so the calculator multiplies net area by the number of coats before dividing by the selected coverage rate.