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Paint calculator
Enter the room, the doors and windows and the coverage printed on the can: the gallons, the exact need and the quarts show while you type.
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Paint to buy
2 gal
1.90 gallons exactly, or 8 quarts
| Wall area | 384 sq ft |
| Doors and windows deducted | 51 sq ft |
| Area to paint, per coat | 333 sq ft |
Manufacturers recommend two coats on bare drywall or for full color; one coat may do over the same color. Textured or porous walls take more. How this is calculated.
A 12 by 12 foot bedroom with 8 foot walls, one door and two windows has 333 square feet of wall to paint, and two coats at 350 square feet per gallon take 1.90 gallons, so you buy 2 gallons; add the ceiling and the need climbs to 2.73, or 3 gallons. The calculator subtracts 21 square feet for each 3 by 7 foot door and 15 for each 3 by 5 foot window, multiplies by the number of coats and divides by the coverage. Its default of 350 sits inside the spread rates on manufacturer data sheets: 400 to 450 square feet per gallon for Benjamin Moore Regal Select, 300 to 400 for Valspar Ultra. Benjamin Moore recommends 2 coats on bare walls and for full color, and Valspar lists one or two. A single coat over the same color needs only 0.95 gallons in that bedroom, which fits in one gallon. Type your price per gallon to see the bill.
Wall area first, then coats, then coverage
Paint is sold by volume but used by area, so every estimate starts with the walls. The perimeter of the room times the wall height gives the gross area: 384 square feet for the 12 by 12 bedroom. Doors and windows come off next (51 square feet for one door and two windows), leaving 333. Multiply by the coats and divide by the coverage on the label, and you have the exact gallons. The calculator rounds up to whole gallons for the main figure and also shows quarts, since a gallon and a quart or two often beats a second full can.
Ceiling height moves the result more than people expect. The same bedroom with 9 foot walls has 381 square feet to cover and needs 2.18 gallons for two coats, against 1.90 at 8 feet.
| Room | Walls to paint | Walls, 2 coats | Walls and ceiling | Gallons to buy |
|---|---|---|---|---|
| 10 x 10 ft | 269 sq ft | 1.54 gal | 2.11 gal | 2 / 3 |
| 10 x 12 ft | 301 sq ft | 1.72 gal | 2.41 gal | 2 / 3 |
| 12 x 12 ft | 333 sq ft | 1.90 gal | 2.73 gal | 2 / 3 |
| 12 x 14 ft | 365 sq ft | 2.09 gal | 3.05 gal | 3 / 4 |
| 14 x 16 ft | 429 sq ft | 2.45 gal | 3.73 gal | 3 / 4 |
| 16 x 20 ft | 525 sq ft | 3.00 gal | 4.83 gal | 3 / 5 |
| 20 x 24 ft | 653 sq ft | 3.73 gal | 6.47 gal | 4 / 7 |
What the coverage number on the can really means
The spread rate on a data sheet assumes the film thickness the maker intends, 3.6 to 4.0 mils wet for Regal Select, on a sound surface. Benjamin Moore lists Regal Select at 400 to 450 square feet per gallon "depending on surface texture and porosity", and Valspar gives Ultra Interior 300 to 400. On the bedroom above, that spread alone moves the need from 1.48 gallons at 450 square feet to 2.22 at 300. Knockdown or orange-peel texture, a roller with a thick nap and fresh patches of joint compound all pull you toward the low end, which is why the calculator starts at 350 rather than at the best case printed on the label.
One coat, two coats, or primer first
Benjamin Moore recommends 2 coats for full color development and on bare substrates, and says previously painted surfaces can take one or two. Valspar lists one or two coats for Ultra, and for drastic color changes or deep, vivid colors it advises a tintable primer first, warning that some bright shades may need an extra coat to hide. In practice, repainting a white wall in a slightly warmer white is often a one-coat job; going from navy to cream is not.
New drywall is its own case. Raw paper and joint compound drink paint unevenly, so the first coat should be a primer made for it. Benjamin Moore’s drywall primer spreads 350 to 450 square feet per gallon. For the 12 by 12 bedroom with its ceiling, one coat of primer at 350 square feet needs 1.36 gallons, before the two finish coats. If you are hanging the board yourself, the drywall calculator uses the same room inputs to count sheets, tape and compound.
Rooms that are not boxes
For an open plan or an L-shaped room, add up the length of every wall you will paint, then enter half of that total as the length and zero as the width, since the calculator doubles length plus width to get the perimeter. Stairwells and cathedral ceilings are easier to measure piece by piece with the square footage calculator (a gable end is a triangle), then divide the total by the coverage yourself. Closets count; built-in shelves and kitchen cabinets do not. Trim, doors and window casings take a different paint, usually a semi-gloss, so price them as a separate small purchase.
Painting it yourself or hiring a painter
Paint is the smaller part of a professional job. BLS counted 225,190 construction and maintenance painters in May 2025, with a mean wage of $26.64 an hour and the middle half between $21.46 and $29.65. A contractor's hourly rate sits above that wage because it carries insurance, travel, drop cloths and profit, and most of the hours go into moving furniture, filling holes, caulking and cutting in. Ask whether a quote includes the paint and which line it uses, then check its gallon count against the one this page gives for your rooms.