Paint calculator: how much paint do I need?
Free paint calculator: gallons and quarts from your own label. No sign-up.
What you're painting
A number on its own is feet.
A number on its own is inches.
What your can says
Coats
AREA TO PAINT
Turn on JavaScript and this works out your paint as you type. The formula is below if you'd rather do it by hand.
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How the paint calculator works
Start with the tape. Type each length the way it reads: 13' 6", 13 ft 6 in, or a plain 13.5. A number on its own means feet for the walls and inches for doors and windows, and the calculator reads every entry back beside its label before it multiplies anything. That's where a window typed as 36 feet instead of 36 inches gets caught, which beats finding out halfway up the ladder.
The walls are the distance around the room times its height: 2 × (length + width) × height. Each door and window you're not painting comes off at the size you measured. We don't plug in a standard door size: closet doors, patio sliders and front doors all differ. The ceiling is length times width, and it stays out until you switch it on.
Then your label takes over. US data sheets print coverage per gallon, usually as a range: Sherwin-Williams' sheet for SuperPaint interior flat says "350-400 sq. ft. per gallon." Type it the way it's printed. The calculator multiplies your area by your coats, divides by the coverage at both ends of the range, and rounds up to whole cans once, at the very end. Assume a flat 400 instead of reading the label, and a 13' 6" by 11' 9" bedroom with 8-foot walls, a door and two windows gets two gallons for two coats, where Behr's low end of 250 needs 2.91.
That last step matters more than it sounds. If the walls and ceiling take the same paint, the calculator adds them before it rounds. In that bedroom, two coats at 350 square feet a gallon, rounding the walls and the ceiling separately buys four gallons. Adding them first buys three.
We keep no coverage figure of our own, and we don't pick your coats or tack on a waste percentage. If you'd rather finish with a quart than open another gallon, add 1 qt as a second can size and the calculator finds the mix that leaves least over.
The arithmetic can't see what's under the old paint. In a home built before 1978, scraping or sanding can release lead dust. Sherwin-Williams' own data sheet sends you to epa.gov/lead before you start. EPA recommends hiring a lead-safe certified contractor for renovation work in a pre-1978 home.
Who this is for
Homeowners about to repaint a bedroom, finish a basement that was just drywalled, or turn over a rental, with the tape-measure numbers in one hand and the store page open in the other.
Anyone holding a painter's quote that says "3 gallons" and wondering whether that fits the room.
Anyone who'd rather buy a quart than keep a nearly full gallon in the garage until the lid rusts shut.
Homeowner questions about paint coverage
How much paint do I need for a 12x12 room?
Two gallons and a quart covers the walls, going by one label we read. A 12 by 12 foot room with 8-foot walls has 384 square feet of wall before the doors and windows come off. At Sherwin-Williams' 350 to 400 square feet per gallon, two coats take 1.92 to 2.19 gallons. Paint the ceiling in the same paint and it's 2.64 to 3.02 gallons, so three gallons and a quart.
How many gallons of paint do I need for a bedroom?
Measure yours, because bedrooms vary more than the question suggests. For one example, a 13' 6" by 11' 9" bedroom with 8-foot walls, one door and two windows has about 363 square feet of wall to paint. At 350 to 400 square feet per gallon, two coats take 1.82 to 2.08 gallons. That's two gallons, or two and a quart at the low end. Put the ceiling in the same paint and three gallons covers both at either end.
How much does a gallon of paint cover?
Whatever its label says, and labels disagree. Sherwin-Williams prints 350 to 400 square feet per gallon for SuperPaint flat, Benjamin Moore 400 to 450 for Regal Select eggshell, and Behr 250 to 400 for Premium Plus eggshell, "depending on application method and substrate porosity." Behr ties the ends to film thickness: 6.4 mils wet at 250, 4.0 at 400. That checks out. A gallon is 231 cubic inches, and spread four thousandths of an inch thick, it covers about 401 square feet.
Should I buy a quart or a gallon of paint?
Buy whole gallons for most of the job, and a quart to finish when the last gallon would mostly sit on a shelf. A quart is a quarter of a gallon: at 400 square feet a gallon, it covers about 100 square feet in one coat. A 13' 6" by 11' 9" bedroom with a door and two windows needs 2.08 gallons for two coats at 350. Three gallons leave 0.92 over; two and a quart leave 0.17. Price both, because least left over isn't always least money.
How many coats of paint do I need?
We don't pick that for you, and the arithmetic can't either. Benjamin Moore lists "1 or 2" recommended coats for Regal Select. Sherwin-Williams says a coat of primer improves hiding when repainting involves a drastic color change. Until you choose, the calculator shows one, two and three coats side by side: for a 13' 6" by 11' 9" bedroom with a door and two windows, at 350 square feet a gallon, that's two, three and four gallons.
How many coats of paint on new drywall?
Two, on both sheets we read, when the paint is its own primer. Sherwin-Williams' SuperPaint sheet says "Self-prime use 2 coats" on drywall, or one coat of primer and two of paint. Behr calls Premium Plus self-priming: the "first coat is the primer and the second coat is the finish." If you prime separately, the primer has its own label and its own coverage, so count it as a separate paint.
How much paint do I need for a ceiling?
Length times width, then treat it like a wall: area times coats, divided by the coverage per gallon. If the ceiling gets the same paint as the walls, add the two before you round. In a 13' 6" by 11' 9" bedroom with a door and two windows, two coats at 350 square feet a gallon, the walls need 2.08 gallons and the ceiling 0.91. Round each one and you buy four gallons. Add them first and it's three.
What do I do with leftover paint?
Keep a little for touch-ups, and don't wash the rest away. Sherwin-Williams' sheet is blunt: "Do not pour unused contents down the drain." In California, Colorado, Connecticut, Illinois, Maine, Maryland, Minnesota, New York, Oregon, Rhode Island, Vermont, Washington and the District of Columbia, PaintCare runs paint drop-off sites under state paint stewardship laws. Anywhere else, the same sheet's advice holds: ask your local authorities about disposal and recycling.
How much paint do I need?
Area, coats, coverage, then whole cans. Measure each room's walls as 2 × (length + width) × height, take off what you won't paint, and add the ceiling if it's getting the same paint. Multiply by your coats. Divide by the square feet per gallon on the label, at both ends if it prints a range. That's your gallons, and you round up once, at the end.
A paint calculator is only as honest as the coverage figure buried in it, which is why ours carries none. Type your label's figure and you'll see the gallons to two decimals, the same amount in liters, and how much of the last can you'd actually use. If that last can would be mostly full, a quart may finish the job.
Sources and last checked
Checked October 8, 2026. Data version paint-us-2026-10-07.
- Unit definitions: NIST Handbook 44 (2026), Appendix C: 4 quarts = 1 gallon = 231 cubic inches = 128 fluid ounces = 3.785411784 liters; 1 inch = 2.54 centimeters.
- Coverage figures quoted in the answers above: Sherwin-Williams SuperPaint Interior Latex Flat product data sheet (08/2026); Benjamin Moore Regal Select Interior Paint, Eggshell, product page; Behr Premium Plus Interior Eggshell Enamel No. 2050 technical data sheet (05/25).
- Paint drop-off: PaintCare's list of paint stewardship states.
- Lead: US EPA, Lead Renovation, Repair and Painting Program.
The calculator does plain arithmetic on the numbers you type. We name the makers for what they print on their own sheets, and we don't recommend one over another.
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