How Much Paint Do You Need? Coverage Rates Explained
September 18, 2026
One gallon of standard interior paint typically covers 350-400 square feet with one coat — but most projects need two coats, and doors, windows, and trim should be subtracted from your wall area before calculating.
Skip the math and get your answer instantly:
Open the Paint Calculator →The Basic Formula
Paint Needed = (Total Wall Area − Openings) / Coverage per Gallon. For a room with 400 sq ft of wall area minus 40 sq ft of doors and windows: 360 sq ft ÷ 350 sq ft/gallon ≈ 1.03 gallons per coat — round up to 1 gallon, or size up if doing two coats in one purchase.
Why Coverage Rates Vary
Coverage of 350-400 sq ft per gallon assumes a smooth, previously painted surface. Textured walls, new drywall, or a significant color change (dark to light or vice versa) reduce effective coverage and often require an extra coat or a primer coat, both of which increase total paint needed beyond the basic formula.
How Many Coats Do You Actually Need?
Most interior repaints in a similar color need 2 coats for even coverage. A significant color change (especially going lighter over a darker existing color) often needs a primer coat plus 2 topcoats. Budget for 2 coats as the default assumption unless you're confident 1 coat will fully cover.
Frequently Asked Questions
How much wall does one gallon of paint cover?
Typically 350-400 square feet per coat on a smooth, previously painted surface — textured or new drywall surfaces reduce effective coverage.
Do I need to subtract doors and windows from my paint calculation?
Yes — subtract the square footage of doors, windows, and any other unpainted openings from your total wall area before calculating how much paint you need.
How many coats of paint do most rooms need?
Two coats is standard for even, durable coverage in most interior repaints — a major color change may also need a primer coat first.
Does ceiling paint need to be calculated separately from wall paint?
Yes — ceilings typically use flat paint formulated differently from wall paint, and should be calculated as a separate area (room length × width) rather than combined with the wall square footage.
Why does my paint seem to cover less than the can claims?
Textured surfaces, unprimed new drywall, and significant color changes all reduce effective coverage below the can's stated rate, which assumes an ideal smooth, similarly-colored surface.