Wall paint comes in gallon cans and quarts, and the label prints how much area a gallon covers. Makers print 200 to 450 square feet per gallon for interior wall paint, for each coat. The calculator starts at 400 square feet, so swap in the figure on the can you plan to buy.
How to use this calculator
- Measure the room's length and width at floor level, and the wall height from the floor to the ceiling. Use the tallest height if the ceiling is uneven. For an L-shaped room, run each rectangle separately and add the gallons. The square footage calculator can help you find the floor area of each part.
- Enter the doors and windows on the walls you will paint. Then open More options and measure a door and a window, width times height, and enter those areas. The starting areas are only guesses, so use your own figures.
- Set the coats to the number you plan to apply. The calculator starts at 2 coats, and most makers recommend 1 to 2 coats. Also replace the coverage per gallon under More options with the figure on your can.
- Choose walls only, or walls and ceiling, and set the primer coat to yes if the walls need one.
- Read the buy list. It rounds the wall paint, and any ceiling paint or primer, up to whole gallon cans and quarts. Buy everything in one order and check the batch numbers, since shades can shift between batches.
Worked examples
Bedroom walls
Room: 12 × 14 ft · Wall height: 8 ft · Doors: 1 · Windows: 2 · Coats: 2
- Wall paint
- 1.83 gallons
- Gallon cans
- 2
- Wall area to paint
- 366 sq ft
- Taken off for doors and windows
- 50 sq ft
Living room with ceiling
Room: 16 × 20 ft · Wall height: 8 ft · Doors: 2 · Windows: 3 · Coats: 2 · Paint: Walls + ceiling · Area of one door: 21 sq ft · Area of one window: 12 sq ft
- Wall paint
- 2.49 gallons
- Gallon cans
- 2
- Quarts
- 2
- Gallon cans of ceiling paint
- 2
- Wall area to paint
- 498 sq ft
- Taken off for doors and windows
- 78 sq ft
- Ceiling
- 320 sq ft
- Ceiling paint
- 1.6 gallons
Small bathroom
Room: 6 × 8 ft · Wall height: 8 ft · Doors: 1 · Windows: 1
- Wall paint
- 0.945 gallons
- Gallon can
- 1
- Wall area to paint
- 189 sq ft
- Taken off for doors and windows
- 35 sq ft
New drywall, primed first
Room: 12 × 12 ft · Wall height: 8 ft · Doors: 1 · Windows: 1 · Primer coat: Prime first
- Wall paint
- 1.75 gallons
- Gallon cans
- 2
- Gallon can of primer
- 1
- Wall area to paint
- 349 sq ft
- Taken off for doors and windows
- 35 sq ft
- Primer
- 0.873 gallons
Gallons of wall paint for common room sizes, by number of coats
| Room | Coats: 1 | Coats: 2 |
|---|---|---|
| 10 × 10 ft | 0.675 | 1.35 |
| 12 × 12 ft | 0.835 | 1.67 |
| 12 × 16 ft | 0.995 | 1.99 |
| 15 × 20 ft | 1.28 | 2.55 |
Each cell: Wall paint (gallons). Inputs not in the table use the calculator's starting values.
How the gallon count is built
The calculator adds the room's length and width, adds them again for the distance around the room, and multiplies that by the wall height. It takes off the doors and windows, multiplies the rest by the number of coats, and divides by the coverage per gallon.
The headline shows the gallons before rounding. The buy list rounds the wall paint up to whole cans and quarts, since stores sell paint in those sizes. Leftover paint is listed in quarts, but a large leftover rounds up to a whole gallon can instead.
Doors, windows and the ceiling
Doors and windows come off the wall area, so their sizes change the count. Measure each one as its width times its height, and enter those areas under More options.
Choose walls and ceiling to paint the ceiling too. The calculator uses the room's floor area as the ceiling area and figures ceiling paint at 400 square feet per gallon. Makers print 400 to 450 square feet per gallon for ceiling paint, and the calculator uses the low end of that range, so it errs toward more paint.
Priming and what uses more paint
Prime new drywall, bare patches and repaired walls, because bare board and fresh filler are porous and soak up paint unevenly. Set the primer coat to yes and the calculator adds primer gallons for the walls, plus the ceiling if you chose it. A water-based primer is rated at 400 to 450 square feet per gallon, and the calculator uses 400 square feet per gallon. New drywall also needs its sheet count from the drywall calculator.
Rough, porous or patched walls soak up paint, so they take more than smooth, sealed ones. A big color change or a dark color over a light one can need extra coats, and each coat adds to the count. If you expect a poorer finish, lower the coverage under More options and the gallons rise to match.
Mistakes to avoid
- Buying for a single coat when the job needs more. Set the coats to the number you plan to apply.
- Using the starting coverage without checking the can. The count depends on the figure printed on the paint you buy.
- Measuring only the floor. The wall height changes the count, so measure it from the floor to the ceiling.
- Ordering paint for a wall that will be papered. Paper is ordered in rolls, so count those with the wallpaper calculator.
Common questions
How do I calculate how much paint I need?
Multiply the room's perimeter by the wall height, subtract the doors and windows, then multiply by the coats and divide by the coverage per gallon. The calculator does these steps and rounds up to whole cans and quarts.
How many square feet does a gallon of paint cover?
Makers print 200 to 450 square feet per gallon for interior wall paint, for each coat. The calculator starts at 400 square feet, but use the figure on your can. Rough or porous walls can cover less.
Will a single gallon cover a small square room?
It depends on the wall height, the openings and the coats, so the floor size alone does not settle it. Enter the room's length, width and height, and check the gallon cans line.
What is the formula for calculating paint?
Wall paint in gallons equals the wall area times the number of coats, divided by the coverage per gallon. The wall area is the perimeter times the wall height, minus the doors and windows. Ceiling paint follows the same pattern with the floor area.
Will one gallon of paint cover a 10x10 room?
For a small room like this, one gallon usually covers a single coat of wall paint but not two. A gallon covers 400 square feet per coat, and most makers recommend 1 to 2 coats. Enter your room in the calculator and check the gallon cans line to see if one can is enough.