Paint calculator
Enter the room's length, width and wall height, the doors and windows, and the number of coats. The calculator takes the openings off the wall area and divides by the coverage on the can, in US gallons or litres.
Paint calculator
Each 3 ft × 6 ft 8 in (20 ft²).
Each 3 × 5 ft (15 ft²).
Two for a color change; one may do for a refresh in the same color.
Use the figure on your can. Rough or bare surfaces cover less.
Paint to buy
2.09 gal
Walls, unfolded
Where the area comes from
The formula
- Wall area: the room's perimeter × wall height, that is 2 × (length + width) × height.
- Less openings: take off each door and window. The calculator counts a door as 3 ft × 6 ft 8 in (20 ft²) and a window as 3 × 5 ft (15 ft²); in metric, 0.9 × 2.1 m and 1.2 × 1.2 m.
- Times coats: usually two.
- Divide by coverage: the area one gallon (or litre) covers in one coat, from the can. Round up.
Worked example
A 14 × 12 ft room with 8 ft walls: 2 × (14 + 12) × 8 = 416 ft² of wall. Take off one door (20 ft²) and two windows (30 ft²): 366 ft². Two coats is 732 ft², and 732 ÷ 350 = 2.09 gallons. Buy 3 gallons, or 2 gallons and a quart if you are sure of the coverage. The ceiling, 168 ft², needs about another gallon for two coats, usually of a separate ceiling paint.
| Room | Doors and windows | Wall area to paint | Gallons | Buy |
|---|---|---|---|---|
| 10 × 10 ft | 1 and 1 | 285 ft² | 1.63 | 2 gal |
| 10 × 12 ft | 1 and 1 | 317 ft² | 1.81 | 2 gal |
| 12 × 12 ft | 1 and 2 | 334 ft² | 1.91 | 2 gal |
| 12 × 14 ft | 1 and 2 | 366 ft² | 2.09 | 3 gal |
| 14 × 16 ft | 1 and 2 | 430 ft² | 2.46 | 3 gal |
| 16 × 20 ft | 2 and 3 | 491 ft² | 2.81 | 3 gal |
In metric, a 4 × 3 m room with 2.5 m walls, one door and one window has 31.7 m² to paint; two coats at 8.5 m² per litre is about 7.5 litres.
Primer, trim and the rest
- Primer goes on new drywall, patches and big color changes; count it as one more coat at the primer's own coverage.
- Trim and doors are usually a different sheen. A quart covers the trim of a typical room; a door and frame take roughly a quart for two coats on both sides.
- Leftover paint is worth keeping for touch-ups; note the color code and sheen on the lid.
Every room at once
For a whole house, a floor plan saves the measuring. FloorGen's Schedules and budget panel (in the account menu) works out each room's wall area from its inside perimeter and wall height, net of its doors and windows, and the Budget section multiplies it by a rate you enter. See materials estimate from a floor plan for a worked house.
Questions
How much paint do I need for a 12 × 12 room?
With 8 ft walls, one door and two windows, about 334 ft² of wall: 1.9 gallons for two coats at 350 ft² per gallon, so 2 gallons. The ceiling is another 144 ft² a coat.
How many square feet does a gallon of paint cover?
Most interior wall paints state 350 to 400 ft² per gallon for one coat on a smooth, primed surface. Rough or bare surfaces take more paint; use the number on your can.
Should I subtract doors and windows?
Yes for a standard door or window; that is what this calculator does. A small window barely changes the total, but a room with a patio door and three windows is noticeably less paint.
Do I need two coats?
Usually, for an even finish and for any change of color. One coat may be enough when you repaint in the same color over a sound surface.