How Much Paint Do I Need? A Room-by-Room Guide
Buying too little paint means a second trip to the store and a risk of a slightly different batch. Buying too much wastes money. The good news is that the amount you need comes from a short calculation, and a typical bedroom needs about two to three gallons.
The quick answer
A gallon of paint usually covers around 350 to 400 square feet of smooth wall with one coat. For a standard 12 × 12 ft room with 8 ft ceilings, two coats on the walls need roughly two gallons. If you also paint the ceiling, plan on about three.
Step by step
- Measure the walls. Add the length and width of the room, double it, then multiply by the ceiling height. A 12 × 14 ft room with 8 ft ceilings has 2 × (12 + 14) × 8 = 416 square feet of wall.
- Subtract the openings. A standard door is about 20 square feet and a standard window about 15. One door and two windows remove 50, leaving 366.
- Add the ceiling if you are painting it. Length times width, so 168 square feet for this room.
- Multiply by the number of coats. Two coats on 366 square feet cover 732 square feet.
- Divide by the coverage on the can. At 350 square feet per gallon, 732 ÷ 350 is about 2.1 gallons.
- Add 10%. This covers touch-ups and paint left in the tray and roller, giving about 2.3 gallons. Buy three gallons, or two gallons and two quarts.
Paint needed for common room sizes
These figures assume one door, two windows, two coats and 350 square feet per gallon, with no extra added.
| Room | Walls only | Walls + ceiling |
|---|---|---|
| 10 × 10 ft, 8 ft ceiling | 1.5 gal | 2.1 gal |
| 12 × 12 ft, 8 ft ceiling | 1.9 gal | 2.7 gal |
| 12 × 14 ft, 8 ft ceiling | 2.1 gal | 3.1 gal |
| 14 × 16 ft, 8 ft ceiling | 2.5 gal | 3.7 gal |
| 15 × 20 ft, 9 ft ceiling | 3.3 gal | 5.0 gal |
What changes the amount
- The surface. Rough, textured or unprimed surfaces absorb more paint than smooth, sealed ones, so the coverage on the can is optimistic for them.
- The colour change. Going from a dark wall to a light one, or the other way round, can need a primer and extra coats.
- The paint itself. Coverage differs between brands and finishes, so use the figure printed on the can you plan to buy.
- Trim and doors. These are not in the wall estimate. A quart is often enough for the trim of a small room.
Common mistakes
The most frequent error is calculating from the floor area instead of the wall area. Another is forgetting that two coats double the amount. Finally, leaving out the extra margin can leave you a little short on the last wall.
Skip the arithmetic with the Paint Calculator, which handles doors, windows, coats, the ceiling and metric units.
Frequently asked questions
How much paint do I need for a 12 × 12 room? About 2 gallons for the walls with two coats, or about 3 gallons if you also paint the ceiling, based on 350 square feet per gallon and one door and two windows.
Do I need to subtract windows and doors? It is more accurate to subtract them. A standard door is about 20 square feet and a window about 15, and large windows make a real difference.
How many coats do I need? Two is the usual number. A single coat can work when repainting a similar colour, but a big colour change or bare drywall often needs a primer plus two coats.
How much extra paint should I buy? About 10% more than the calculation gives you room for touch-ups and paint lost to the tray and roller.