Figure My Build

Paint Calculator

Enter the room, tell us about doors, windows and coats, and get a practical shopping answer in gallons and quarts, not a decimal you have to guess at in the store aisle.

Diagram of a wall showing its length and height, with a door and a window
One wall at a time: length × height is the area every wall material covers.

Your buy-list

Enter your measurements

How the paint quantity is calculated

Wall area is the room perimeter × ceiling height. We then subtract the parts you don't paint, using the figures in manufacturer estimating guides: 21 sq ft per door and 15 sq ft per window. Add the ceiling area (length × width) if you're painting that too.

Gallons = paintable area × number of coats ÷ coverage per gallon. Manufacturers quote 350–400 sq ft per gallon for one coat. Sherwin-Williams and PPG around 400, Benjamin Moore and Behr around 350. We default to 350 so you don't run short, and you can change it to match your paint can.

The buy recommendation converts the exact figure into whole gallons plus quarts (a quart covers a quarter of a gallon's area), so a room needing 2.16 gallons reads as "2 gallons + 1 quart" instead of forcing you to buy 3 full gallons. Covering the walls with paper instead? The Wallpaper Calculator counts double rolls by pattern repeat.

Sources

The figures behind this calculator come from published manufacturer data and industry standards:

Worked examples

12 × 12 ft bedroom, 8 ft ceiling

1 door, 2 windows, 2 coats, no ceiling. 333 sq ft of wall.

Buy 2 gallons

10 × 15 ft living room, 9 ft ceiling

2 doors, 2 windows, 2 coats. 378 sq ft of wall.

Buy 2 gallons + 1 quart

5 × 8 ft bathroom, 8 ft ceiling

1 door, no windows, 2 coats, ceiling included. 227 sq ft total.

Buy 1 gallon + 2 quarts

Frequently asked questions

How much paint do I need for a 12×12 room?
Walls only, 8 ft ceilings, a door and two windows, two coats: about 1.9 gallons: buy 2 gallons. Including the ceiling adds about 0.8 gallons of paint (144 sq ft × 2 coats), so the buy total becomes 2 gallons + 3 quarts.
How many square feet does a gallon of paint cover?
350–400 sq ft per coat depending on the brand. Check the can. Rough, porous or unpainted surfaces drink more; budget closer to 300 sq ft per gallon there.
Do I really need two coats?
For a durable, even finish over a different colour, yes: plan on two. Same-colour refreshes over sound paint can sometimes get away with one, but the second coat is what makes it look finished.
Should I buy primer separately?
On new drywall, bare wood or over stains, primer is its own product and its own coat. Budget roughly the same coverage as one coat of paint. Paint-and-primer-in-one still needs primer on bare surfaces.
Why does the calculator suggest quarts?
Because paint is cheaper bought precisely. A result like 2 gallons + 1 quart saves you most of a third gallon's price while still leaving a little spare for touch-ups.

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Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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