Paint Calculator
This paint calculator works out how many gallons you need to paint a room. Enter the room size and ceiling height, take off the doors and windows, and pick your coats, and you'll get the gallons to buy along with the paintable square footage. It uses the standard 350 square feet per gallon, which you can change to match your paint can.
- Gallons for a room
- Doors & windows removed
- Any coverage & coats
- Optional ceiling
- Live as you type
Last updated July 30, 2026 1 gallon ≈ 350 sq ft per coat Built by Muhammad Younus
Enter the room size above 0.
Doors count as ~21 sq ft and windows ~15 sq ft. Estimate for planning; buy a little extra for touch-ups.
312 ft² × 2 coats ÷ 350 = 1.78 → 2 gallons
How much paint do I need?
Paint is sold by coverage, so the job comes down to area. Find the wall area by multiplying the room's perimeter by the ceiling height, subtract the doors and windows you won't paint, then divide by the coverage on the can, usually about 350 square feet per gallon. Multiply by the number of coats, and round up to whole gallons, since you can't buy a fraction of a can. Take a 12 by 12 room with 8-foot walls: that's 384 square feet, and after openings and two coats it lands near 2 gallons. The calculator runs all of that the moment you type, so you'll know what to buy before you're at the store.
Working out a room, step by step
Here's how the calculator handles a 12 by 12 room with 8-foot ceilings, one door and two windows, two coats. It's the same path you'd take by hand, just faster:
- 1
Find the wall areaPerimeter is 2 × (12 + 12) = 48 ft, times the 8-foot height, so 384 square feet of wall.
- 2
Subtract the openingsOne door (21) and two windows (30) remove 51 square feet, leaving 333 to paint.
- 3
Divide by coverage333 ÷ 350 is about 0.95 gallons for a single coat.
- 4
Multiply by coats and round upTwo coats is 1.9 gallons, so you'll buy 2 gallons.
How coats and coverage change the total
Two numbers drive the amount: how many coats you apply and how far the paint spreads. Two coats is standard for an even, lasting finish, and it's basically double the paint of a single coat. Coverage varies by paint and surface, since a smooth primed wall takes the full 350 square feet a gallon, while bare drywall or a rough texture drinks more and you'll get less out of the can. A bold color change over a dark wall often needs an extra coat too, so don't skimp there. Set both above to match your job, and you'll see the gallons shift. To measure the room first, the square footage calculator gives you the floor and wall areas.
How many gallons of paint by room size
Want a number before you measure? This chart runs the calculator's own math for common rooms, all with 8-foot ceilings, two coats, one door and two windows removed, at 350 square feet per gallon. Your walls may differ, so treat it as a starting point and fine-tune the size above.
| Room size | Wall area | After openings | Paint (2 coats) |
|---|---|---|---|
| 10 × 10 ft | 320 sq ft | 269 sq ft | 2 gallons |
| 10 × 12 ft | 352 sq ft | 301 sq ft | 2 gallons |
| 12 × 12 ft | 384 sq ft | 333 sq ft | 2 gallons |
| 12 × 15 ft | 432 sq ft | 381 sq ft | 3 gallons |
| 14 × 16 ft | 480 sq ft | 429 sq ft | 3 gallons |
| 16 × 20 ft | 576 sq ft | 525 sq ft | 3 gallons |
| 20 × 24 ft | 704 sq ft | 653 sq ft | 4 gallons |
Gallons of paint by paintable square footage
If you already know the surface area you're covering, read straight down this chart. It's the paintable square footage, not a home's floor size, so a 1,500-square-foot house has much more wall than the 1,500 row shows. Both columns come from dividing the area by 350 and rounding up to whole cans.
| Paintable area | One coat | Two coats |
|---|---|---|
| 250 sq ft | 1 gallon | 2 gallons |
| 500 sq ft | 2 gallons | 3 gallons |
| 750 sq ft | 3 gallons | 5 gallons |
| 1,000 sq ft | 3 gallons | 6 gallons |
| 1,250 sq ft | 4 gallons | 8 gallons |
| 1,500 sq ft | 5 gallons | 9 gallons |
| 2,000 sq ft | 6 gallons | 12 gallons |
Paint coverage by surface
A gallon doesn't stretch the same on every wall. Smooth, primed drywall gets the full 350 to 400 square feet, while rough, porous surfaces drink far more. Match your surface below, then set the coverage box above so the gallons reflect the real job.
| Surface | Coverage per gallon | Notes |
|---|---|---|
| Smooth, primed drywall | 350 to 400 sq ft | The 350 default fits most repaints. |
| New or textured drywall | 300 to 350 sq ft | Fresh drywall and texture soak up more. |
| Wood siding | 250 to 300 sq ft | Grain and gaps cut the spread. |
| Brick or masonry | 200 to 250 sq ft | Rough, porous face needs extra. |
| Stucco | 150 to 200 sq ft | Deep texture is the thirstiest surface. |
| Primer | 200 to 300 sq ft | Thinner build than topcoat. |
Want the cost, can sizes, and litre and weight math too? Our how much paint do I need guide walks through pricing and room-by-room charts in full.
Frequently asked questions
How much paint for a 12x12 room?
With 8-foot walls, a 12 by 12 room is about 384 square feet, so roughly 1 gallon for one coat or 2 gallons for two coats, a touch less once you remove the door and windows. That's a common size, which is why 2 gallons covers most bedrooms.
Measure the wall area, subtract doors and windows, then divide by the coverage of your paint, usually about 350 square feet per gallon, and multiply by the number of coats. A 12 by 12 room with 8-foot walls has 384 square feet, and after two coats it needs roughly 2 gallons. This paint calculator does that for you, so you'll buy close to the right amount.
Coverage is how far a gallon stretches, printed on the can as square feet per gallon. Most interior wall paints cover about 350 square feet in one coat, though primers and rough surfaces cover less. Divide your paintable area by the coverage to get gallons per coat, then multiply by the coats. The calculator above uses 350 by default, and you can change it to match your paint.
Two coats is the norm for a durable, even finish, and it's what most pros quote. One coat works for a small color refresh over a similar shade, while a big color change, a patchy wall, or bare drywall wants two coats over primer. Set the number of coats above and the gallons update, since each extra coat adds the same amount of paint again.
Often, for one coat of a small to mid-size room. A gallon covers about 350 square feet, which is roughly the walls of a 10 by 10 room. For two coats, or a larger space, you'll want two gallons. Buying by the gallon is cheaper per square foot than quarts, so round up to the next gallon unless you only need a touch.
Yes, for a tighter estimate. A standard door is about 21 square feet and an average window about 15, so a couple of each removes 70-plus square feet from the total. On a small room that's nearly a quarter of a wall, enough to change whether you need a second gallon. The calculator subtracts them once you enter the counts.
A ceiling takes its area, length times width, divided by the same 350-square-foot coverage. A 12 by 12 ceiling is 144 square feet, so under half a gallon for one coat, though ceilings often want two. Tick the ceiling option above to fold it into the total, since ceiling and wall paint are usually bought separately.
For 1,500 square feet of surface to paint, plan on about 5 gallons for one coat or 9 gallons for two, at 350 square feet per gallon. Note that's paintable area, not a home's floor size: a 1,500-square-foot house has far more wall than 1,500 square feet, so measure the actual walls or enter the room above. Porous surfaces like stucco or brick push the count higher.
A gallon covers about 350 to 400 square feet of smooth, primed drywall in one coat, which is the 350 default here. New or textured drywall drops to roughly 300 to 350, wood siding 250 to 300, and porous stucco just 150 to 200, since rough surfaces drink more paint. Check your can, since the printed coverage is what you should type into the coverage box.
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