Paint Calculator
How many gallons of paint a room needs, walls and ceiling, with doors, windows and coats taken into account.
Paint needed
1.90
gallons
1.90 gallons for 333 sq ft of wall in 2 coats.
What to buy
- Gallon cans
- 2 cans
- Or quart cans (small jobs)
- – quarts
Breakdown
- Walls
- 1.90 gal
- Ceiling
- – gal
- Wall area (openings removed)
- 333 sq ft
- Ceiling area
- – sq ft
Cost
- Paint
- –
How much paint do I need?
Multiply the room's perimeter by the wall height, subtract about 21 sq ft per door and 15 sq ft per window, multiply by the number of coats, and divide by the coverage on the can, typically 250 to 400 sq ft per gallon. A 12 × 12 ft room with 8 ft walls, one door and two windows needs about 1.90 gallons for two coats, so buy 2 gallons.
Worked example: a 12 × 12 ft bedroom, two coats
- Walls: perimeter 48 ft × 8 ft = 384 sq ft.
- Openings: minus one door (21) and two windows (30) = 333 sq ft.
- Coats: 333 × 2 = 666 sq ft of painting.
- Gallons: 666 ÷ 350 sq ft per gallon = 1.90 gallons, so buy 2 gallon cans.
Paint for common rooms (two coats)
One door and two windows, 350 sq ft per gallon.
| Room | Walls only | Walls and ceiling |
|---|---|---|
| 10 × 10 ft, 8 ft walls | 1.54 gal (buy 2) | 2.11 gal (buy 3) |
| 12 × 12 ft, 8 ft walls | 1.90 gal (buy 2) | 2.73 gal (buy 3) |
| 12 × 14 ft, 8 ft walls | 2.09 gal (buy 3) | 3.05 gal (buy 4) |
| 15 × 20 ft, 9 ft walls | 3.31 gal (buy 4) | 5.02 gal (buy 6) |
Getting the coverage right
- Read the can. Behr rates its paints at 250 to 400 sq ft per gallon. Use the number on your can.
- Rough or porous surfaces such as new drywall, bare plaster or textured walls soak up more paint. Prime new drywall first.
- Big color changes, especially light over dark, may need a primer or a third coat.
- Trim and doors are usually done in a different finish; a quart covers the trim in most rooms.
Buying tips
- Round up to whole gallons. Running out halfway through a wall can leave a visible line.
- Four gallons or more? A 5-gallon bucket is often cheaper per gallon and keeps the color consistent.
- Keep the leftovers for touch-ups, labelled with the room and the color name.
Frequently asked questions
How much area does a gallon of paint cover?
Usually 250 to 400 sq ft per coat, depending on the paint and the surface. Behr lists this range; check your can for the exact figure.
How many gallons of paint for a 12 × 12 room?
With 8 ft walls, one door, two windows and two coats: about 1.9 gallons, so 2 gallons. Add about 0.8 gallons if you paint the ceiling too.
Do I need two coats of paint?
Usually, for a new color or for even coverage. One coat can be enough when repainting the same color or with a high-hiding paint over a similar shade.
How do I calculate paint for a ceiling?
Multiply the room's length × width for the ceiling area, multiply by the number of coats, and divide by the coverage per gallon. A 12 × 12 ceiling with two coats at 350 sq ft per gallon needs about 0.82 gallons.
Should I subtract doors and windows?
Yes, for larger openings. A standard door is about 21 sq ft and a typical window about 15 sq ft. Skip tiny ones; the extra paint covers touch-ups.
Related calculators
Drywall CalculatorDrywall sheets, screws, tape and joint compound for a room, with cost.Square Footage CalculatorSquare feet of any room or area, in sq ft, sq yd, m² and acres.Flooring CalculatorBoxes of laminate, vinyl or hardwood flooring, plus underlayment and baseboard.Tile CalculatorHow many tiles and boxes for a floor, wall or backsplash, grout joints included.
Sources and method
- Behr — how much paint do I need? — each gallon covers 250–400 sq ft
Last checked October 12, 2026. How we build and test every calculator: methodology.