Enter your room size and this calculator tells you how many gallons of paint to buy, how many quarts to add, and what the paint will cost.
How the paint calculator works
Paint is sold to cover an area, so the calculator first finds the area you will actually paint, then divides by what one gallon covers.
Paintable area = wall area − doors − windows (+ ceiling if included)
Gallons = paintable area × coats ÷ coverage per gallon
A standard interior door takes out about 21 square feet (3 × 7 ft) and an average window about 15 square feet (3 × 5 ft). Most interior wall paints cover 350 to 400 square feet per gallon on smooth drywall, which is why 350 is the default: it builds in a small margin.
Worked example: a 12 × 12 bedroom
The perimeter is 48 feet. With 8-foot walls that is 384 square feet of wall. Take away one door (21) and two windows (30) and you have 333 square feet. Two coats means 666 square feet of coverage. Divided by 350, that is 1.9 gallons, so you buy 2 gallons.
How much paint for common room sizes
Two coats, 8-foot walls, one door, two windows, 350 square feet per gallon, walls only:
| Room size | Paintable walls | Paint needed | What to buy |
|---|---|---|---|
| 10 × 10 ft | 269 sq ft | 1.5 gal | 2 gallons |
| 12 × 12 ft | 333 sq ft | 1.9 gal | 2 gallons |
| 12 × 14 ft | 365 sq ft | 2.1 gal | 2 gallons + 1 quart |
| 14 × 16 ft | 429 sq ft | 2.5 gal | 2 gallons + 2 quarts |
| 16 × 20 ft | 525 sq ft | 3.0 gal | 3 gallons |
| 20 × 20 ft | 589 sq ft | 3.4 gal | 3 gallons + 2 quarts |
What paint costs in 2026
Shelf prices for interior latex paint fall into three rough bands. Prices change with sales and region, so use the price field above for the can you are actually buying.
| Grade | Typical price per gallon | Best for |
|---|---|---|
| Budget / contractor grade | $25–$35 | Rentals, closets, ceilings, quick refreshes |
| Mid-grade | $40–$55 | Most bedrooms and living areas |
| Premium | $60–$90 | Kitchens, hallways, kids’ rooms, one-coat color changes |
A premium paint that covers in one coat can cost less overall than a budget paint that needs three. The bar chart in the calculator shows that trade-off for your room.
Tips that save paint and money
- Buy it all at once. Tinted batches can vary slightly. If you need several gallons, pour them together in a bucket (“boxing”) before you start.
- Adjust coverage for texture. Textured, porous or never-painted walls soak up more paint. Set coverage to 250–300.
- Prime for big color changes. Going from red to white? One coat of tinted primer usually saves a coat of paint.
- Keep a labeled quart. Touch-ups years later are easy when you still have the exact color.
Frequently asked questions
How many square feet does a gallon of paint cover?
Most interior paints cover 350 to 400 square feet per coat on smooth, previously painted walls. Rough or bare surfaces can drop that to 250–300. The exact figure is printed on the can.
Do I really need two coats?
Usually, yes. Two coats give even color and hide roller marks. One coat can work when you repaint the same color with a good paint.
How much paint do I need for 1,000 square feet of wall?
About 5.7 gallons for two coats at 350 square feet per gallon, so buy 6 gallons.
How much paint does a ceiling need?
A ceiling is simply length × width. A 12 × 12 ceiling is 144 square feet, under half a gallon per coat. Choose “Yes” for ceiling in the calculator to include it.
Should I subtract doors and windows?
Yes for accurate numbers. In a small room the savings are minor, but in a room with a large window wall it can save a gallon.
