How many gallons of paint do you need?
Enter your room size to get the amount of paint to buy, with the math shown so you can check it.
How the paint calculator works
The calculator finds the wall area you will actually paint, multiplies it by the number of coats, and divides by how far one gallon of paint spreads. It then adds a little extra so you do not run short.
Paintable area = wall area − doors − windows
Gallons = paintable area × coats ÷ coverage per gallon × (1 + extra for waste)
The result is rounded up to the next quart, because stores sell paint by the quart and the gallon. If you also add the ceiling or primer, each one is figured separately with its own coverage. The full list of assumptions is on the methodology page.
Example: how much paint for a 12 × 12 room?
Take a 12 by 12 foot room with 8-foot ceilings, one door and two windows, painted with two coats. These are the numbers the calculator starts with.
| Step | Math | Result |
|---|---|---|
| Wall area | 2 × (12 + 12) × 8 | 384 sq ft |
| Doors and windows | 1 × 21 + 2 × 15 | 51 sq ft |
| Paintable area | 384 − 51 | 333 sq ft |
| Paint for 2 coats | 333 × 2 ÷ 350 | 1.90 gal |
| Extra for waste (10%) | 1.90 × 1.10 | 2.09 gal |
| To buy | Rounded up to the next quart | 2 gal + 1 qt |
Other room sizes are worked out on the paint by room size page.
What changes how much paint you need
- Wall surface. Smooth, previously painted drywall lets paint spread the furthest. Textured walls, new drywall and other porous surfaces soak up more, so a gallon covers less. See how much a gallon of paint covers.
- Color change. Covering a dark color with a light one often takes a tinted primer plus two coats, or three coats without primer.
- Primer. Primer usually covers less area per gallon than paint. It helps on new drywall, stains and bare wood.
- Number of coats. Two coats is the common recommendation. One coat can be enough when you repaint the same color over walls in good shape.
- Finish. Some manufacturers list lower coverage for glossier finishes. The label on your can is the best guide.
Buying tips
- Read the coverage printed on the can and pick "My paint can says something else" if it differs from the presets.
- Buy all the paint for one room at the same time. Batches can vary slightly, which can show up as a color difference on the wall.
- Keep a sealed quart for touch-ups if you have room to store it.
- Measure floor to ceiling. For a vaulted ceiling, use the average wall height.
Common questions
How many gallons of paint do I need for a 12 × 12 room?
With 8-foot ceilings, one door, two windows and two coats, the walls need about 2 gallons, which this calculator rounds to 2 gallons and 1 quart with a 10% allowance for waste. Add the ceiling separately if you are painting it.
How much does a gallon of paint cover?
Retailers commonly give 350 to 400 square feet per coat on smooth walls. Rough or porous surfaces cover less, and primer commonly covers 200 to 300 square feet per gallon. Your paint can lists the manufacturer's figure.
Do I subtract doors and windows?
Yes. This calculator subtracts 21 square feet for a standard 3 × 7 ft door and 15 square feet for a standard 3 × 5 ft window. Other calculators use slightly different sizes, so results can differ a little. For a sliding door or a large picture window, count it as more than one, or change the sizes under Advanced settings.
How many coats of paint do I need?
Plan on two coats for most rooms, and choose three if you are going from a dark color to a light one without primer.
Do I need primer?
Primer is usually worth it on new drywall, bare wood, stains, and big color changes. If you are repainting a similar color over clean, sound walls, you can often skip it.
How much paint do I need for a ceiling?
Ceilings are figured on their own: length × width, then divided by coverage. Most ceilings get one coat unless there are stains to cover. Tick "Paint the ceiling too" to add it to your total.
Can I use this for exterior painting?
No. Siding, brick and stucco take paint differently from interior walls and need different coverage numbers. This tool is built for interior rooms.