Measure the room or the wall, count the doors and windows — or give the whole house's square footage, or its outside walls. You get how much paint to buy, in the cans it is sold in.
Paint to buy
2 gallonsfor 2 coats on 334 sq ft of wall
Quick answer: one gallon of paint covers about 350–400 sq ft of smooth wall per coat, and most walls need two coats. To find how much paint you need, multiply the room’s perimeter by the wall height. Take off about 20 sq ft for each door and 15 for each window, double it for two coats, and divide by 350. A 12 × 12 ft room with 8 ft walls takes 2 gallons. The calculator above does it for your room, in the gallons and quarts paint is sold in. For a whole house it works from the square footage: a 2,000 sq ft home with 10 rooms and 8 ft walls takes about 24 gallons for the walls, 12 of ceiling white and 2 of trim white. For the outside, a 50 × 30 ft one-story house with vinyl siding takes about 13 gallons of body color for two coats, 2 gallons and a quart of trim, and a quart for the front door. Rough stucco takes about three times the body paint.
How to use the paint calculator
- Choose a whole room, one wall, the whole house or the outside. For a room, enter the floor’s length and width; for an accent wall, its width; for the house, its square footage and how many rooms you paint; for the outside, the house’s length and width, its stories, its gables and its siding.
- Enter the wall height from the floor to the ceiling, and count the doors and windows.
- Pick the coats and the surface. Two coats is the usual; textured, rough or porous walls take more paint.
- Add the ceiling or primer if you need them. They are listed separately, because they are different cans.
- Read what to buy: gallons and quarts, the exact amount, and the square footage behind it. Copy link takes the list to the store.
The rules the calculator uses
How many square feet a gallon of paint covers
Most interior paint cans say 350–400 sq ft per gallon, per coat, on a smooth, primed wall. The calculator uses 350, the low end, because rollers, edges and touch-ups always use a little more than the label. Textured, rough or porous walls, like fresh plaster or unprimed drywall, drink more: about 250–300 sq ft per gallon, so the calculator uses 275. A quart is a quarter of a gallon and covers about 90 sq ft.
How to work out the wall area
For a room, add the four wall lengths (the perimeter) and multiply by the wall height. A 12 × 12 ft room with 8 ft walls has 48 × 8 = 384 sq ft of wall. Take off what you are not painting: about 20 sq ft for a door and 15 sq ft for a window. One door and two windows leave 334 sq ft.
How many coats of paint
Two coats is the rule for an even finish. One coat is enough only when you repaint in the same color over paint in good condition. Three coats may be needed for a big change, like white over deep red. A coat of primer and then two coats of paint often does that job better and costs less.
How much primer
Primer goes on in one coat and covers a little less than paint: about 300 sq ft per gallon on smooth walls and 250 on textured ones. Use it on new drywall, bare wood, patched areas, stains, and when going from a dark color to a light one.
How much paint to paint a house interior
A house’s square footage is its floor, not its walls, and no paint maker prints a rule to turn one into the other: two homes of the same size can have very different amounts of wall. So the calculator says how it counts. It takes your floor area and how many rooms you paint, and treats every room as a square of the average size. A 2,000 sq ft home with 10 rooms has rooms of about 200 sq ft, 14.1 ft on a side: 56.6 ft of wall each, 566 ft in all, and 4,525 sq ft of wall at 8 ft high. Twelve doors and fourteen windows take off 450 sq ft, leaving 4,075 sq ft. Two coats need 23.29 gallons: 24 gallons, best bought as 5-gallon buckets. Long, narrow or L-shaped rooms have more wall than a square, so if your rooms are like that, measure the biggest ones with “A whole room”.
A whole-house palette has two more paints, and the calculator counts both. The ceiling white covers every ceiling, which together is the floor area: 2,000 sq ft, two coats, 12 gallons. The trim white covers a 4¼-inch baseboard along every room’s walls and 2¼-inch casing round both faces of every door and round every window: 319 sq ft here, two coats, 2 gallons. The doors themselves are extra: about 21 sq ft a face.
How much paint to paint a house exterior
The calculator follows Behr’s own method for the outside. The body is the perimeter times the height from the foundation to the roofline, gables left out: about 10 ft for one story and 9 ft more for each story above. Each gable, the triangle of wall under the roof’s peak, adds half its width times its height. The calculator puts the gables on the narrow ends of the house at a 6-in-12 roof, so a 30 ft wide end rises 7.5 ft and adds 113 sq ft. Take off 15 sq ft for each window and 20 for each door, Behr’s averages, and 63 sq ft for each garage door (9 × 7 ft).
A 50 × 30 ft one-story house has 160 ft × 10 ft = 1,600 sq ft of wall, plus 225 sq ft of gables. Twelve windows, two doors and a garage door take off 283, leaving 1,542 sq ft. On vinyl siding, two coats need 12.34 gallons: 13 gallons, best bought as two 5-gallon buckets and three single gallons. Two stories with sixteen windows take 24 gallons.
The siding decides how far a gallon goes. Exterior paint makers print a range, and the calculator uses the low end, as it does indoors:
| Siding | Sq ft per gallon, one coat | What the makers print | The 50 × 30 ft house, 2 coats |
|---|---|---|---|
| Vinyl or aluminum, fiber cement, smooth wood | 250 | Benjamin Moore Aura Exterior 250–350; Sherwin-Williams Duration Exterior 250–300 | 13 gallons |
| Wood shakes, shingles, rough-sawn wood | 200 | Sherwin-Williams: “Rough Sawn 200-300 sq. ft. per gallon” | 16 gallons |
| Smooth stucco, brick or block | 200 | Sherwin-Williams Loxon Acrylic Coating: “200 sq. ft. per gallon” | 16 gallons |
| Rough or textured stucco | 80 | Loxon: “Coverage on porous & rough stucco 80 square feet per gallon” | 39 gallons |
The trim is counted the same way, at Behr’s average width of six inches: the fascia along every roof edge, the corner boards on siding that has them, and the casing round every window and door. The calculator adds the garage doors to it, painted with the trim: about 280 sq ft on the house above, 2 gallons and a quart. Behr’s rule of thumb, a gallon of trim for every eight of body, lands close. The front door in its own color is one face of 20 sq ft: a quart covers it twice. Not chosen the colors yet? Try the body color on a photo of your house with the Exterior House Color Visualizer, then the window trim with the Exterior Trim Color Picker.
How paint is sold, and how the calculator rounds
Paint comes in quarts, gallons and 5-gallon buckets. Two quarts usually cost about as much as a gallon, so the calculator adds at most one quart, and rounds anything more up to a gallon. Within a tenth of a gallon of a whole can, the cans you already have will cover it. Buying all the paint for a room at once also keeps the color identical from can to can.
How much paint for a room: chart
8 ft walls, one door, two windows, two coats, smooth walls:
| Room | Wall area to paint | Wall paint | Ceiling paint |
|---|---|---|---|
| 10 × 10 ft | 270 sq ft | 2 gallons | 1 gallon |
| 10 × 12 ft | 302 sq ft | 2 gallons | 1 gallon |
| 12 × 12 ft | 334 sq ft | 2 gallons | 1 gallon |
| 12 × 14 ft | 366 sq ft | 2 gallons | 1 gallon |
| 14 × 16 ft | 430 sq ft | 3 gallons | 2 gallons |
| 16 × 20 ft | 526 sq ft | 3 gallons | 2 gallons |
| 20 × 20 ft | 590 sq ft | 4 gallons | 3 gallons |
Paint coverage per can
| Can | Smooth wall, one coat | Textured wall, one coat |
|---|---|---|
| Quart | about 90 sq ft | about 70 sq ft |
| Gallon | 350–400 sq ft | 250–300 sq ft |
| 5-gallon bucket | 1,750–2,000 sq ft | 1,250–1,500 sq ft |
Five worked examples
A 12 × 14 ft bedroom with primer. With 8 ft walls, one door and two windows, there are 366 sq ft to paint. Two coats need 2.09 gallons, which is 2 gallons: 350 sq ft is the low end of what a gallon covers, so the last tenth is covered. Priming the walls first takes 1 gallon and 1 quart of primer.
An accent wall, 12 ft wide and 8 ft high. That is 96 sq ft, and two coats need just over half a gallon. Two quarts would cost about as much as a gallon, so buy 1 gallon. The rest is useful for touch-ups.
A 16 × 20 ft living room with 9 ft ceilings. With two doors and three windows, there are 563 sq ft to paint. Two coats need 3.22 gallons: 3 gallons and 1 quart.
A 1,200 sq ft home with 6 rooms. With 8 ft walls, seven doors and nine windows, there are 2,440 sq ft of wall. Two coats need 13.94 gallons: 14 gallons of wall paint, 7 gallons of ceiling white for 1,200 sq ft of ceiling, and 1 gallon of trim white for 192 sq ft of baseboard and casing.
The outside of a 40 × 24 ft ranch. One story, two gables, two doors, twelve windows, no garage, vinyl siding: 128 ft × 10 ft = 1,280 sq ft of wall, plus 144 sq ft of gables, less 220 for the doors and windows, leaves 1,204 sq ft. Two coats need 9.63 gallons: 10 gallons, two 5-gallon buckets. The trim takes 2 gallons and the front door 1 quart.
Common paint-buying mistakes
- Measuring the floor instead of the walls. A 12 × 12 room has 144 sq ft of floor but 384 sq ft of wall at 8 ft high. A whole house has about twice as much wall as floor.
- Planning one coat. A single coat almost always shows roller marks and patches. Plan for two.
- Buying one can at a time. Tints can vary slightly between batches. Buy the room’s paint together, and mix the cans in a bucket if you have more than one.
- Using wall paint on the ceiling. Ceiling paint is flatter and spatters less. It is its own line on the list.
- Skipping primer on new drywall. Bare drywall soaks up the first coat unevenly. One coat of primer saves paint.
Read next
- Can you use the same paint for walls and ceilings?
- Flat or satin paint for the ceiling
- Paint colors for small rooms
- Living room paint color ideas
- A geometric accent wall painting tutorial
Paint questions
How much paint to paint a house interior?
About 24 gallons for the walls of a 2,000 sq ft home with 10 rooms and 8 ft walls, two coats, plus 12 gallons of ceiling white and 2 of trim white. A 1,200 sq ft home with 6 rooms takes about 14 gallons for the walls. Choose “The whole house” above and type your square footage and rooms.
How many square feet does a gallon of paint cover?
About 350–400 sq ft per coat on a smooth, primed wall, and about 250–300 sq ft on a textured or porous one. For two coats, halve it: a gallon paints roughly 175–200 sq ft of wall twice.
How much paint do I need for a 12×12 room?
2 gallons for two coats on 8 ft walls, with one door and two windows: 334 sq ft of wall. Add 1 gallon of ceiling paint if you are painting the ceiling too.
How much paint for a bedroom?
Most bedrooms, from 10 × 10 ft to 12 × 14 ft with 8 ft walls, take 2 gallons for two coats. A larger bedroom, 14 × 16 ft, takes 3 gallons.
How much does a quart of paint cover?
About 90 sq ft of smooth wall in one coat, a quarter of what a gallon covers. That is enough to paint a small wall, a door or a piece of furniture, but not an accent wall in two coats.
How many coats of paint do I need?
Two for an even finish. One is enough only when you repaint the same color over sound paint. A big color change can need three, or one coat of primer and two coats of paint.
How many coats of primer do I need?
One coat on most surfaces. Two can help on raw wood, heavy stains, or when covering a very dark color with a light one.
How much paint do I need to paint the outside of a house?
About 13 gallons of body color for two coats on a 50 × 30 ft one-story house with vinyl siding, plus 2 gallons and a quart of trim and a quart for the front door. Two stories take about 24 gallons. Rough stucco takes about three times as much, because it covers only 80 sq ft a gallon. Choose “The outside” above and enter your house.
Choosing colors for the whole room? Try your layout and furniture in the free 2D planner before you paint.
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