Why paint cans are misleading
Every paint can lists a coverage rate, but that number assumes ideal conditions — a smooth, previously painted wall in good shape. Real walls rarely match that exactly, which is why estimating gallons needed is more of a range than a single number.
What changes your real coverage
- Unprimed drywall or new plaster soaks up significantly more paint than a previously painted wall — expect 20-30% lower coverage on the first coat.
- Textured surfaces (orange peel, knockdown, brick) increase surface area beyond what the flat square footage suggests.
- Dark-to-light color changes often need an extra coat regardless of what the can promises.
Two coats is the default for a reason
Most professional painters apply two coats even when a product claims “one-coat coverage,” simply because lighting and viewing angle reveal thin spots that looked fine while wet. Budgeting for two coats from the start avoids a frustrating mid-project paint run.
A simple way to avoid running short
Buy your calculated amount, but ask if your paint store will accept an unopened return — that way you can round up without worrying about waste if you overestimate.
About the formula: Gallons = (Area × Number of coats) ÷ Coverage per gallon, rounded up to the next whole gallon.