CalcKitHome›Home & Auto›Paint calculator
Paint Calculator
Your room
Example: a 12 × 10 ft room with 8 ft ceilings, 1 door and 1 window has 317 sq ft of paintable wall. Two coats at 350 sq ft per gallon need 1.81 gallons, so buy 2 gallons — about $90 at $45 per gallon.
Behind the numbers
How paint coverage works
Paint is sold by the gallon, but walls are measured in square feet. First find the paintable wall area: the perimeter of the room times the ceiling height, minus the area of doors and windows. Then multiply by the number of coats and divide by the coverage on the can. Because paint is only sold in whole gallons, always round up — running out mid-wall is worse than a little leftover for touch-ups.
A standard door is about 21 sq ft (3 × 7 ft) and a typical window about 14 sq ft (3.5 × 4 ft). A 12 × 10 ft room with 8 ft ceilings: 2 × 22 × 8 = 352 sq ft, minus 21 + 14 = 317 sq ft.
317 sq ft × 2 coats = 634 sq ft ÷ 350 sq ft per gallon = 1.81 gallons, so buy 2 gallons.
2 gallons × $45 = $90.
A few comparisons
Worked examples
| Room | Result |
|---|---|
| 12 × 10 ft, 8 ft ceiling, 1 door, 1 window, 2 coats at 350 sq ft/gal | 2 gal · $90 |
| 10 × 12 ft, 9 ft ceiling, 1 door, 2 windows, 1 coat at 350 sq ft/gal | 1 gal · $45 |
| 15 × 12 ft, 8 ft ceiling, 2 doors, 2 windows, 2 coats at 400 sq ft/gal | 2 gal · $90 |
| 500 sq ft of wall, 2 coats at 350 sq ft/gal | 3 gal · $135 |
| 250 sq ft of wall, 1 coat at 350 sq ft/gal | 1 gal · $45 |
| 8 × 8 ft, 8 ft ceiling, 1 door, 1 window, 1 coat at 350 sq ft/gal | 1 gal · $45 |
Paint, without the guesswork.
Always round up to whole gallons. A half-gallon short means a second trip to the store and a visible seam where the new batch starts.
Budget for a second coat when going from a dark color to a light one, or painting bare drywall. The first coat soaks in and the color shows through.
Textured or unprimed walls drink more paint. If your coverage is closer to 250 square feet per gallon, enter that number instead of 350.
Buy all your gallons from the same batch and mix them together in one bucket. It evens out tiny color differences between cans.
Good to know
Your paint questions, answered.
How many gallons of paint do I need for a 12x10 room?
A 12 by 10 foot room with 8 foot ceilings has 352 square feet of wall. After subtracting one door (21 sq ft) and one window (14 sq ft), 317 square feet remain. Two coats need 634 square feet of coverage, which is 1.81 gallons at 350 square feet per gallon, so buy 2 gallons.
How many square feet does one gallon of paint cover?
Most interior paints cover about 350 square feet per gallon on a smooth, primed wall. Rough or unprimed surfaces cover less, often 250 to 300 square feet per gallon, so check the label on your can.
Should I subtract doors and windows when calculating paint?
Yes. A standard interior door is about 21 square feet (3 by 7 feet) and a typical window is about 14 square feet. Subtracting them avoids buying paint for wall that is not there.
How much paint do I need for two coats?
Double the paintable wall area, then divide by the coverage per gallon and round up. For example, 317 square feet times 2 coats is 634 square feet, which needs 2 gallons at 350 square feet per gallon.