The label rate assumes your surface is boring
Manufacturer coverage ratings — commonly 350 to 400 sq ft per gallon — assume smooth, sealed, previously painted surfaces. That is the right constant for repaint work in good condition, and the wrong one for almost everything else.
What eats coverage
- Bare or patched drywall: unsealed paper and compound drink primer and first coats.
- Textured or rough surfaces: more surface area than the flat measurement suggests.
- Dramatic color changes: hiding power, not coverage, becomes the constraint — plan the extra coat.
Estimating with coats, not vibes
Write the system into the scope: primer coat yes or no, finish coat count, and the condition that justifies them. Gallons follow from area × coats ÷ coverage, rounded up. A 1,000 sq ft repaint at two coats and 400 sq ft per gallon is 5 gallons — 6 with a 10% allowance. If the walls turn out to need a third coat, the written scope is what makes that a change order instead of an argument.