To find how much paint you need, multiply the room's perimeter by the wall height, subtract doors and windows, multiply by the number of coats and divide by the coverage on the can (about 350–450 sq ft per gallon). A 12 × 12 ft bedroom with 8 ft walls needs about 1.94 gallons for two coats, so buy 2 gallons.
This paint calculator is for homeowners and painters planning a room, a whole floor or a single accent wall. Enter the room size, or a wall area you have already measured, plus coats and the coverage from your paint's label. It returns gallons, quarts and 5-gallon buckets, a primer quantity, liters and square meters, and an optional cost.
How to use the calculator
- Choose Room size and enter length, width and wall height in feet, or choose Wall area if you already know the square footage.
- Enter how many doors and windows the room has and their size in inches. The calculator subtracts them from the walls.
- Pick whether the ceiling gets the same paint. Ceiling paint is usually a different product, so you can also run the ceiling separately with its own coverage.
- Set the number of coats and the coverage per gallon printed on the can or data sheet. The presets copy the published ranges for two common product lines.
- Add a primer coat if you are covering stains, bare drywall or a much darker color, and a price per gallon if you want a cost.
The formula
Wall area = 2 × (length + width) × height. Net area = wall area − (doors × door width × door height) − (windows × window width × window height), plus length × width if you paint the ceiling. Gallons = net area × coats ÷ coverage per gallon. That is the same method the NEWMOA paint-waste handout gives: measure, use about 400 sq ft per gallon per coat, and multiply by the coats (it gives 400 sq ft, two coats = 2 gallons). The District of Columbia's environment department also tells residents to buy only the paint they need, estimated from square footage, to cut leftover paint.
Containers come in fixed sizes. NIST Handbook 44 defines 4 quarts = 1 gallon, so the calculator rounds up to whole quarts, then shows the purchase as 5-gallon buckets, gallons and quarts. The default coverage is 350 sq ft per gallon, the low end of the Sherwin-Williams range, because real walls are rarely as smooth as a test panel.
How much does 1 gallon of paint cover?
One gallon of interior latex paint covers about 350–450 square feet with one coat. Sherwin-Williams lists 350–400 sq ft per gallon at 4 mils wet for ProMar 200 HP, and Benjamin Moore lists 400–450 sq ft for Regal Select. With two coats a gallon covers 175–225 sq ft of wall. Those numbers answer “how many square feet per gallon of paint” for smooth, sealed drywall; textured or porous surfaces get less.
How much will 5 gallons of paint cover?
Five gallons of paint cover about 1,750–2,250 square feet in one coat, or 875–1,125 square feet in two coats. At 350 sq ft per gallon and two coats, a 5-gallon bucket paints about 875 sq ft, which is the walls of roughly 2.6 12 × 12 ft bedrooms. A bucket makes sense when the calculator says you need more than about 4 gallons of one color.
| Paint | 1 coat @ 350 | 1 coat @ 400 | 2 coats @ 350 | 2 coats @ 400 |
|---|---|---|---|---|
| 1 quart | 88 sq ft | 100 sq ft | 44 sq ft | 50 sq ft |
| 1 gallon | 350 sq ft | 400 sq ft | 175 sq ft | 200 sq ft |
| 2 gallons | 700 sq ft | 800 sq ft | 350 sq ft | 400 sq ft |
| 3 gallons | 1,050 sq ft | 1,200 sq ft | 525 sq ft | 600 sq ft |
| 5 gallons | 1,750 sq ft | 2,000 sq ft | 875 sq ft | 1,000 sq ft |
| 10 gallons | 3,500 sq ft | 4,000 sq ft | 1,750 sq ft | 2,000 sq ft |
Gallons of paint per square foot
Turned around, paint use is coats ÷ coverage gallons per square foot: 0.00286 gal/sq ft for one coat at 350 sq ft per gallon and 0.0025 at 400. Per 100 sq ft, that is 0.29 and 0.25 gallons, or about 1.1 quarts.
| Area | 1 coat @ 350 | 2 coats @ 350 | 2 coats @ 400 | Buy (2 coats @ 350) |
|---|---|---|---|---|
| 100 sq ft | 0.29 gal | 0.57 gal | 0.5 gal | 3 qt |
| 250 sq ft | 0.71 gal | 1.43 gal | 1.25 gal | 1 gal + 2 qt |
| 400 sq ft | 1.14 gal | 2.29 gal | 2 gal | 2 gal + 2 qt |
| 500 sq ft | 1.43 gal | 2.86 gal | 2.5 gal | 3 gal |
| 750 sq ft | 2.14 gal | 4.29 gal | 3.75 gal | 4 gal + 2 qt |
| 1,000 sq ft | 2.86 gal | 5.71 gal | 5 gal | 1 × 5-gal bucket + 3 qt |
| 1,500 sq ft | 4.29 gal | 8.57 gal | 7.5 gal | 1 × 5-gal bucket + 3 gal + 3 qt |
| 2,000 sq ft | 5.71 gal | 11.43 gal | 10 gal | 2 × 5-gal buckets + 1 gal + 2 qt |
| 3,000 sq ft | 8.57 gal | 17.14 gal | 15 gal | 3 × 5-gal buckets + 2 gal + 1 qt |
How many gallons to paint a room
The table assumes 8 ft walls unless stated, 36 × 80 in doors and 36 × 48 in windows (one door per room; two for the larger rooms), two coats and 350 sq ft per gallon. The door and window sizes are examples; enter your own in the calculator.
| Room | Net wall area | Walls, 2 coats | With ceiling | Buy (walls) |
|---|---|---|---|---|
| 10 × 10 ft | 288 sq ft | 1.65 gal | 2.22 gal | 1 gal + 3 qt |
| 10 × 12 ft | 308 sq ft | 1.76 gal | 2.45 gal | 2 gal |
| 12 × 12 ft | 340 sq ft | 1.94 gal | 2.77 gal | 2 gal |
| 12 × 14 ft | 372 sq ft | 2.13 gal | 3.09 gal | 2 gal + 1 qt |
| 14 × 16 ft | 424 sq ft | 2.42 gal | 3.7 gal | 2 gal + 2 qt |
| 16 × 20 ft | 500 sq ft | 2.86 gal | 4.69 gal | 3 gal |
| 12 × 12 ft, 9 ft walls | 388 sq ft | 2.22 gal | 3.04 gal | 2 gal + 1 qt |
| 20 × 24 ft, 9 ft walls | 704 sq ft | 4.02 gal | 6.77 gal | 4 gal + 1 qt |
Worked examples
12 × 12 ft bedroom, walls only
2 × (12 + 12) × 8 = 384 sq ft. Subtract one 3 × 6.67 ft door and two 3 × 4 ft windows (44 sq ft) to get 340 sq ft. Two coats at 350 sq ft per gallon: 340 × 2 ÷ 350 = 1.94 gallons. Buy 2 gallons, or 2 gal.
Same room with the ceiling
The ceiling adds 12 × 12 = 144 sq ft, making 484 sq ft. Two coats need 2.77 gallons. If the ceiling gets a separate flat ceiling white, run it on its own: 144 × 2 ÷ 350 = 0.82 gallons, so 1 gal.
Hallway with 9 ft walls
A 10 × 10 ft area with 9 ft walls, one door and one window has 328 sq ft of wall. Two coats at 400 sq ft per gallon take 1.64 gallons; at 350 it is 1.87. That difference is why the coverage you enter matters.
Priming new drywall
New drywall in the 12 × 12 ft room: one primer coat at 400 sq ft per gallon is 0.85 gallons (1 gal), then two finish coats at 350, 1.94 gallons.
What changes coverage
- Surface. Benjamin Moore's data sheet says its rate depends on surface texture and porosity. Fresh drywall mud, bare plaster, brick and rough-sawn wood soak up paint.
- Film thickness. The Sherwin-Williams figures are for 4 mils wet. Rolling thicker gives better hide but fewer square feet per gallon.
- Color change. Going from dark to light usually takes a primer or an extra coat. Benjamin Moore notes that some custom colors need a tinted deep-base primer.
- Sheen and product. Coverage differs by line and finish, so use the number on your can or data sheet rather than a rule of thumb.
Common mistakes
- Multiplying floor area instead of wall area. A 12 × 12 room has 144 sq ft of floor but 384 sq ft of wall at 8 ft.
- Forgetting the second coat. Benjamin Moore recommends two coats for full color development; plan for two unless you are repainting the same color.
- Entering door sizes in feet. The door and window fields are in inches (36 × 80, not 3 × 6.67).
- Buying the top of the range. 450 sq ft per gallon is a best case. Use the low end for textured or porous walls.
- Mixing batches mid-wall. If you need several gallons of one custom color, buying a bucket or boxing gallons together keeps the color consistent.
Painting the outside? Measure the walls with the siding calculator (it handles gables and openings) and enter that area here with an exterior paint's coverage. Planning the whole room? The flooring calculator handles the floor, the renovation cost calculator the budget, and the linear feet calculator trim and baseboard.
Frequently asked questions
How much paint do I need for a 12 × 12 room?
About 1.94 gallons for two coats on the walls of a 12 × 12 ft room with 8 ft walls, one 36 × 80 in door and two 36 × 48 in windows (340 sq ft of wall) at 350 sq ft per gallon. Buy 2 gallons, or 2 gal with less left over. Adding the ceiling (144 sq ft) raises it to 2.77 gallons.
How many square feet does 1 gallon of paint cover?
One gallon covers 350–400 sq ft per coat for Sherwin-Williams ProMar 200 HP and 400–450 sq ft for Benjamin Moore Regal Select, according to their data sheets. Two coats halve that: 175–225 sq ft of wall.
How much will 5 gallons of paint cover?
A 5-gallon bucket covers 1,750–2,250 sq ft with one coat at 350–450 sq ft per gallon, or 875–1,125 sq ft with two coats. At 350 sq ft per gallon and two coats that is 875 sq ft, enough for the walls of about 2.6 rooms of 12 × 12 ft.
How many gallons of paint per square foot?
At 350 sq ft per gallon, one coat uses 0.0029 gallons per square foot, and two coats 0.0057. It is easier to divide your area by the coverage: 1,000 sq ft × 2 coats ÷ 350 = 5.71 gallons.
How many gallons to paint a room?
Most bedrooms need 2–3 gallons for two coats on the walls. A 16 × 20 ft living room with 8 ft walls, two doors and three windows needs 2.86 gallons (3 to buy) at 350 sq ft per gallon. Use the calculator for your exact size.
Should I subtract doors and windows?
Yes, if you want to buy close to what you use. A 36 × 80 in door is 20 sq ft and a 36 × 48 in window is 12 sq ft. In the 12 × 12 ft example they remove 44 of 384 sq ft (11%). Measure your own; these sizes are examples, not standards.
How many quarts are in a gallon of paint?
Four. NIST Handbook 44 defines 4 quarts = 1 gallon = 231 cubic inches, and 1 gallon = 3.785 liters. A quart covers about a quarter of a gallon's area: 88–112.5 sq ft per coat.
Do I need primer?
Benjamin Moore says Regal Select is self-priming on most properly prepared surfaces, but recommends two coats on bare substrates. Stains, glossy surfaces and big color changes often need a separate primer. Sherwin-Williams lists 400 sq ft per gallon for its ProMar 200 primer, so one primer coat on 340 sq ft takes 0.85 gallons.
Why does my paint cover less than the can says?
Data-sheet spread rates assume a smooth, sealed surface at the stated wet film thickness (4 mils wet for the Sherwin-Williams figures). Benjamin Moore notes coverage depends on surface texture and porosity, and the NEWMOA handout warns that dry porous walls need more. New drywall, stucco, rough wood and deep colors all lower real coverage.
Is this a Benjamin Moore paint calculator?
No. FreeFast is not affiliated with Benjamin Moore or Sherwin-Williams. The calculator lets you enter any coverage figure; the 400–450 and 350–400 sq ft presets are copied from their published data sheets so you can compare.
Sources & method
- Benjamin Moore — Regal Select Interior Paint Matte (N548) Technical Data Sheet: spread rate 400–450 sq ft per gallon
- Sherwin-Williams — ProMar 200 HP Zero VOC Interior Acrylic Eg-Shel (B20W02951) Product Data Sheet, 07/2025: 350–400 sq ft per gallon
- Sherwin-Williams — ProMar 200 Zero VOC Interior Latex Primer (B28W02600) Product Data Sheet: 400 sq ft per gallon
- NEWMOA / Maine latex paint handout — one gallon covers about 400 sq ft per coat; porous walls need more
- District of Columbia DOEE — How to Manage Leftover Paint: buy only the paint you need, estimated from square footage
- NIST Handbook 44 (2026), Appendix C — 4 quarts = 1 gallon = 231 in³; 1 gal = 3.785 411 784 L
Results are estimates for general information. Found an error? It helps everyone — see our methodology.