Calculator · Paint
Paint Calculator: How Much Paint Do I Need for a Room?
Enter the room, the doors and windows, the coats and the kind of wall, and get how many gallons of paint and primer to buy, split into the cheapest mix of quarts, gallons and 5-gallon buckets. Coverage comes from the paint makers' data sheets.
Materials ticket · Paint
Enter the room or the area and your shopping list prints here.
How to calculate how much paint you need
- Find the wall area. Add the lengths of all the walls (the perimeter) and multiply by the wall height.
- Subtract doors and windows. About 20 ft² for a standard 36 × 80 in door and 15 ft² for a 3 × 5 ft window. Measure yours if they are bigger.
- Multiply by the coats and divide by the coverage. Most walls take two coats at 350–400 ft² per gallon.
Check it with a published example: HomeGuide says a 12 × 12 ft room with 8 ft ceilings needs about 2 gallons for two coats on the walls. The calculator gives 1.99 gallons.
Paint for common rooms
Two coats at 350 ft² per gallon, 8 ft walls unless noted, doors of 20 ft² and windows of 15 ft². "Buy" is the cheapest mix at the middle of HomeGuide's price ranges.
| Room | Wall area | Wall paint | Buy | Ceiling paint |
|---|---|---|---|---|
| Small bathroom, 5 × 8 ft, 1 door, no window | 188 ft² | 1.1 gal | 1 gal + 1 qt | 0.2 gal |
| Bedroom, 10 × 12 ft, 1 door, 1 window | 317 ft² | 1.8 gal | 2 gal | 0.7 gal |
| Bedroom, 12 × 12 ft, 1 door, 1 window | 349 ft² | 2 gal | 2 gal | 0.8 gal |
| Primary bedroom, 14 × 16 ft, 2 doors, 2 windows | 410 ft² | 2.3 gal | 3 gal | 1.3 gal |
| Living room, 14 × 20 ft, 9 ft walls, 2 doors, 3 windows | 527 ft² | 3 gal | 3 gal + 1 qt | 1.6 gal |
| Kitchen, 12 × 14 ft, 2 doors, 1 window | 361 ft² | 2.1 gal | 2 gal + 1 qt | 1 gal |
Gallons for two coats by surface
| Area | Smooth, painted (400 ft²/gal) | Typical (350 ft²/gal) | Textured or porous (250 ft²/gal) |
|---|---|---|---|
| 100 ft² | 0.5 gal | 0.6 gal | 0.8 gal |
| 250 ft² | 1.3 gal | 1.4 gal | 2 gal |
| 500 ft² | 2.5 gal | 2.9 gal | 4 gal |
| 1,000 ft² | 5 gal | 5.7 gal | 8 gal |
| 2,000 ft² | 10 gal | 11.4 gal | 16 gal |
Coverage: what the data sheets say
- Sherwin-Williams SuperPaint Interior: 350–400 ft² per gallon at 4 mils wet. On new drywall, two coats of the paint alone, or one coat of primer and two of paint.
- Behr Premium Plus Interior: 250–400 ft² per gallon; the range depends on texture, porosity and how it is applied.
- KILZ 2 All-Purpose primer: 300–400 ft² per gallon, depending on the application method and how porous the surface is.
That is why the calculator asks about the surface: a smooth, already painted wall reaches the top of the range, while textured walls, bare drywall, brick or stucco soak up paint and land at the bottom. HomeGuide also notes that drastic color changes may need extra coats.
Quarts, gallons or 5-gallon buckets
HomeGuide puts a quart at $15–$40, a gallon at $20–$60 (interior) and a 5-gallon bucket at $75–$300. Per gallon, quarts are the most expensive way to buy paint, so a quart only makes sense to top up the last bit. The calculator tries every mix and keeps the cheapest one that covers what you need; enter your store's prices under "Prices" to get your own answer.
For a whole house exterior, HomeGuide estimates 5 to 25 gallons depending on the size of the house and the number of coats. Use the "I know the ft²" option with the wall area of each side.
Frequently asked questions
How much paint do I need for a 12 × 12 room?
About 2 gallons for two coats on the walls, with 8 ft walls, one door and one window: 349 ft² of wall at 350 ft² per gallon. HomeGuide gives the same answer, about 2 gallons. The ceiling adds 0.8 gallons for two coats.
How many square feet does a gallon of paint cover?
350–400 ft² per coat for Sherwin-Williams SuperPaint, according to its data sheet, and 250–400 ft² for Behr Premium Plus, depending on the texture and porosity of the surface. Rough, porous or bare surfaces soak up more, so plan on the low end for them.
How many coats of paint do I need?
Two, in most cases. Sherwin-Williams calls for two coats on new drywall and notes that priming plus two coats helps when you are covering an old color. One coat can be enough when you repaint the same color, and HomeGuide notes that a drastic color change may need extra coats.
Do I need primer before painting?
On new drywall, stains, bare wood or a big color change, yes: Sherwin-Williams recommends a coat of primer in those cases. Primer covers a bit less than paint: KILZ 2 lists 300–400 ft² per gallon.
How much does a gallon of paint cost?
HomeGuide puts interior paint at $20–$60 a gallon and exterior paint at $30–$80. A 5-gallon bucket runs $75–$300, and a quart $15–$40, so quarts are the most expensive way to buy paint by volume.
Should I buy a 5-gallon bucket or single gallons?
Compare the price per gallon at your store. At the middle of HomeGuide's ranges, a 5-gallon bucket ($188) costs less than five single gallons ($200), but more than four. The calculator picks the cheapest mix of buckets, gallons and quarts that covers what you need, with the prices you enter.
Sources
- Sherwin-Williams SuperPaint Interior Latex Flat, product data sheet 101.02A (08/2026)paintdocs.com
- BEHR PREMIUM PLUS Interior Paint & Primer: 250–400 sq. ft. per gallonbehr.com
- KILZ 2 All-Purpose Primer: 300–400 sq. ft. per gallon, depending on application and porositykilz.com
- HomeGuide: How much does a gallon of paint cost? (June 23, 2025)homeguide.com
- HomeGuide: How much paint do I need? (March 12, 2025)homeguide.com