Free Tool
Enter the wall area you're painting, the number of coats, and your paint's coverage. Get the exact gallons of paint and primer to buy — with door and window deductions so you never over-order. Free for homeowners and pros.
Works in square feet · adjust coverage to your product's label
Gallons = net area × coats ÷ coverage, rounded up. Net area subtracts 21 ft² per door and 15 ft² per window.
Measure your walls, plug in the numbers, and walk into the paint store knowing exactly how many gallons to grab — no half-finished walls, no leftover cans stacking up in the garage.
Turn a measurement into a materials count on the spot, add your unit price for an instant cost, and quote with confidence. In ServicePros Hub, the same calculation drops straight into a proposal.
First we find your net paintable area by subtracting openings — a standard door is about 21 ft², a typical window about 15 ft². Then it's simple.
Gallons = (net area × coats) ÷ coverage, always rounded up to the next full gallon.
Most interior wall paints cover roughly 350 ft² per gallon per coat, but that varies by product, surface texture, and color change — check your can's label and adjust the coverage field. Primer typically covers a bit less (around 300 ft²/gal), so we calculate it separately when you turn it on. Two coats is standard for a durable, even finish, especially over a color change.
A gallon of interior wall paint covers about 350 square feet in one coat on a smooth, primed surface. Rough or porous surfaces (new drywall, stucco, textured walls) absorb more and reduce coverage — lower the coverage number to match. Always check your specific product's label.
Two coats is the standard for a durable, even finish and is almost always required when changing colors or painting over new drywall. A single coat may work for a light refresh of the same color. This calculator defaults to two coats.
Yes — for larger jobs it prevents over-buying. Enter the count of each and the calculator deducts 21 ft² per door and 15 ft² per window from the paintable area. For a rough estimate on a small room, you can leave them at zero.
Multiply each wall's width by its height and add them together, then subtract doors and windows using the fields above. For a quick rectangular-room estimate, add the room's length and width, double it, and multiply by ceiling height.
Add a primer coat for new drywall, bare wood, patched areas, stain-blocking, or big color changes (especially dark-to-light). Turn on "Include a primer coat" and the calculator estimates primer gallons separately at its own coverage rate.
This calculator is one of the trade tools inside ServicePros Hub — proposals, scheduling, invoicing, and card payments for home-service pros. One flat price. No tiers, no add-ons.
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