Free calculator
Paint Calculator by Room: Gallons for Walls and Ceilings
Free paint calculator: wall area from room size and ceiling height, minus doors and windows, then gallons by coats and coverage.
Rooms
- ftftft
- ftftft
- ftftft
On the can; 350–400 is typical.
3' × 7' allowance.
3' × 5' allowance.
Result
Paint needed
5.4gal
Buy 6 gallons
- Wall area
- 953 sq ft
- Coats
- 2
By room
- Living room (441 sq ft)2.5 gal
- Bedroom (325 sq ft)1.9 gal
- Bathroom (187 sq ft)1.1 gal
Walls and ceilings are usually different paints, so each is rounded up to whole gallons on its own. Primer covers less; figure it separately.
How it's calculated
Gallons = (perimeter × ceiling height − doors − windows) × coats ÷ coverage per gallon. A 12 × 11.5 ft bedroom with 8 ft ceilings: 47 × 8 = 376 sq ft, less one door (21) and two windows (30) = 325 sq ft. Two coats at 350 sq ft per gallon is 1.86 gallons, so buy 2 gallons.
How to use the paint calculator
Add each room with its length, width and ceiling height, and count the doors and windows. Feet and inches work (11' 6"). Tick Paint the ceilings too to add ceiling area, then set the number of coats and the coverage printed on your can. The result shows gallons per room, the total, and how many gallons to buy, with walls and ceilings rounded up separately because they're usually different paints.
Paint for common room sizes
8 ft ceilings, one door and two windows, two coats at 350 sq ft per gallon, walls only:
| Room | Wall area | Gallons | Buy |
|---|---|---|---|
| 10 × 10 ft | 269 sq ft | 1.5 | 2 gallons |
| 12 × 12 ft | 333 sq ft | 1.9 | 2 gallons |
| 12 × 15 ft | 381 sq ft | 2.2 | 3 gallons |
| 15 × 20 ft | 509 sq ft | 2.9 | 3 gallons |
| 20 × 20 ft | 589 sq ft | 3.4 | 4 gallons |
With 9 ft ceilings, wall area goes up by one-eighth of the gross wall: a 12 × 12 room gains 48 sq ft. For several rooms in one color, adding first and rounding once saves paint: three rooms that each need 1.4 gallons need 4.2, which is 5 gallons bought together, not 6 bought room by room.
How far does a gallon go?
| Surface | Coverage per gallon | Notes |
|---|---|---|
| Smooth, previously painted walls | 350–400 sq ft | The typical figure on the can. |
| Rough, textured or porous surfaces | Less, down to about 250 sq ft | Texture has more surface to cover. |
| Primer on new drywall | About 200–300 sq ft | Bare paper and joint compound soak it up. |
The calculator defaults to 350 sq ft per gallon, a cautious figure for ordinary walls. Brushing and rolling by hand and cutting in around trim all use a little more than the label suggests.
Doors, windows and trim
The calculator takes off 21 sq ft per door and 15 sq ft per window. Those are typical allowances, not exact sizes: a 3' 0" × 6' 8" door is exactly 20 sq ft, and a sliding patio door or picture window can be several times a standard window. Edit the allowances under the room list, or measure the actual openings for a tighter number. Doors, casings and baseboards are usually painted in a different sheen, and estimated separately.
For a whole house, measuring every room by hand is the slow part. FloorFigures measures rooms from the floor plan, free, and gives wall area less openings and paint gallons per room. See how much paint do I need for a full walkthrough, or the wall area calculator for area alone.
Updated · FloorFigures
Questions
- How much paint do I need for a 12x12 room?
- With 8 ft ceilings, a 12 by 12 room has 384 square feet of wall. Taking off one door (21 sq ft) and two windows (15 sq ft each) leaves 333 square feet. Two coats at 350 square feet per gallon is 1.9 gallons, so buy 2 gallons for the walls. The ceiling adds 144 square feet, about 0.8 gallon for two coats.
- How many square feet does a gallon of paint cover?
- Usually 350–400 square feet per coat on smooth, previously painted walls; Sherwin-Williams gives that range, and Behr lists 250–400 depending on the surface. Rough, textured or porous surfaces take more paint, and primer covers less, about 200–300 square feet per gallon. Use the figure on your can.
- Should I subtract doors and windows when calculating paint?
- Yes, for an accurate count. A common allowance is 21 square feet per door and 15 per window. Those are rules of thumb: a standard 3 ft by 6 ft 8 in door is exactly 20 square feet, and windows vary a lot. Measuring the actual openings is more accurate, especially for patio doors and large windows.
- How much paint do I need for a ceiling?
- A ceiling's area is the room's length times width. A 12 by 14 ft ceiling is 168 square feet; two coats at 350 square feet per gallon is 0.96 gallon, so 1 gallon covers it. Ceiling paint is usually a different product from wall paint, so figure and buy it separately.
- Do I need two coats of paint?
- Two coats is the usual plan for an even finish, and it's what most coverage estimates assume. One coat can be enough when repainting the same color with a good paint. A big color change, a dark color, or new drywall usually needs primer plus two coats.
Skip the typing. Measure the plan.
Open the floor plan in FloorFigures and every room is measured for you, with the same math per room. Try it free on a sample plan; nothing is uploaded.