The key is coated area: net paintable surface multiplied by the number of coats. Container size comes after the calculation.
01 / Formula
How this is calculated
Gallons = (net surface area × coats) ÷ coverage per gallon02 / Assumptions
What the estimate assumes
- ✓Manufacturer coverage is the best starting point.
- ✓Porous or textured surfaces can reduce coverage.
- ✓A little reserve is useful for touch-ups.
03 / Worked example
See the math in context
Four walls totaling 800 sq ft, less 100 sq ft of openings, leave 700 sq ft. Two coats create 1,400 coated sq ft. At 350 sq ft/gal, that is exactly 4 gallons.
04 / Guidance
Measure net wall area
Multiply each wall’s width by height and add the results. Subtract large doors and windows. For rooms, perimeter multiplied by height is a quick gross-wall method.
05 / Guidance
Choose a realistic coverage rate
Use the label for the exact coating. Bare drywall, masonry, rough texture, spraying, or a dramatic color change can move actual usage away from the nominal rate.
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.