Multi-Room Paint Calculator & Shopping List

A paint calculator built for whole projects, not single walls

Most paint calculators answer one room at a time and forget it the moment you leave. That's not how painting actually goes — you're doing the hallway, two bedrooms and maybe the ceiling while the furniture is already shoved into the middle of the house. This calculator keeps a running list of every room, does the gallon math per room, and rolls it all into one shopping list you can print and take to the store. Your project stays saved in your browser, so when you finally get to the second bedroom next weekend, the plan is still here.

The method, step by step

1. Wall area: perimeter × ceiling height. A 12×12 room with 8-ft ceilings has 2 × (12 + 12) × 8 = 384 sq ft of gross wall.
2. Subtract openings: 21 sq ft per door, 15 sq ft per window — the same standard deductions paint stores use. That 384 becomes 348 with one of each.
3. Multiply by coats: two coats means painting the area twice. This is the step most people skip, and it's why "one gallon per room" folklore runs dry halfway along the second wall.
4. Divide by coverage: 350 sq ft per gallon is a fair default for smooth, previously painted drywall. 348 × 2 ÷ 350 ≈ 1.99 gallons — so the shopping list says 2 gallons, not "about 2".
5. Trim and primer ride along separately, because you buy them separately: trim paint by the quart from linear feet of baseboard, primer at one coat and ~300 sq ft per gallon.

What the shopping list rounds — and why

Exact math says things like "2.37 gallons", but stores sell gallons and quarts. The list rounds each total up to the nearest quart and converts four quarts into a gallon, so what you read is what you buy. If the wall total lands just over a whole gallon — say 2.05 — you'll see 2 gallons and 1 quart. Whether you actually buy the quart or stretch the gallons is your call; for the spare-paint side of that decision, our guide to how much extra paint to keep for touch-ups has real numbers.

Getting the inputs right

• Coverage is the honest lever. Fresh drywall, plaster patches and textured surfaces absorb more paint. Drop coverage to 250–300 for those, and read what a gallon really covers by surface if you're unsure.
• Count coats realistically. Like-on-like color refreshes sometimes pass with one coat; light over dark almost never does — here's the coat math for dark walls.
• Trim linear feet: walk the baseboard with a tape measure, or use the room perimeter as a decent stand-in and add door/window casings if you're painting those too.
• Primer is a separate product. The checkbox adds one primer coat over the same area. When you actually need it (bare drywall, stains, drastic color changes) is covered in our primer decision guide.

Frequently asked questions