By the gallon
Paint calculator
Enter your wall or ceiling area, take out the doors and windows, choose your coats, and get the gallons, rounded to cans you can actually buy.
OrderExact · https://orderexact.com/paint/
Coverage by surface
| Surface | Coverage | Notes |
|---|---|---|
| Smooth drywall or plaster | 350–400 sq ft/gal | The figure printed on most cans assumes this surface. |
| Previously painted, similar color | 400 sq ft/gal | Best case. One coat may genuinely be enough. |
| Light texture or orange peel | 300 sq ft/gal | More surface area than it looks. |
| Heavy texture, popcorn, stucco | 200–250 sq ft/gal | Roll slowly and expect to use far more than the can claims. |
| Bare drywall or new plaster | Prime first | Untreated surfaces drink paint. A primer coat is cheaper than a third topcoat. |
Measuring walls quickly
The fast method for a room: add up the length of every wall to get the perimeter, then use that as the length and the ceiling height as the width in a single rectangle above. A 12 by 14 foot room with 8 foot ceilings is a 52 foot perimeter, so 52 × 8 = 416 square feet of wall.
Then subtract openings. The calculator uses 21 square feet per door and 15 per window, which are standard averages. Skip this step for a room with one small window, because it is inside the rounding, but do it for a wall that is mostly glass.
Two coats is the default, not the exception
One coat covers when you are repainting a similar color on a sound surface. Everything else needs two: color changes, bare surfaces, deep or bright colors, and anything where the old finish is glossy.
Big color jumps are better solved with primer than with a third coat. A tinted primer plus two topcoats will look better and cost less than three coats of finish paint.
Buy the whole job at once
Paint is mixed in batches, and two cans tinted weeks apart can differ enough to see on a long wall. Buy all of it in one trip, and if the job is large, ask the store to box it, which means pouring the cans together into one container and stirring, so any variation is spread evenly.
Rounding up is nearly free: an unopened can goes back. Running out at 4pm on a Sunday does not.
Common questions
How much does a gallon of paint cover?
About 350 to 400 square feet on smooth, previously painted walls for a single coat. Textured or bare surfaces can drop that to 200 square feet.
How much does 5 gallons of paint cover?
About 1,750 to 2,000 square feet for a single coat on smooth, previously painted walls, which is 875 to 1,000 square feet of wall at two coats. On texture or bare surfaces expect nearer 1,000 square feet a coat.
What sizes does paint come in?
Quarts, gallons and 5-gallon buckets. A quart is a quarter gallon, which is for touch-ups and samples, not rooms. This calculator buys whole gallons and 5-gallon buckets, and never lets five single cans stand in for a bucket that holds the same and costs less.
How many gallons do I need for a 12x12 room?
With 8 foot ceilings that is 384 square feet of wall, less about 36 square feet for a door and a window. Two coats needs roughly 2 gallons.
Do I subtract doors and windows?
Yes for anything significant. Use about 21 square feet per door and 15 per window. On a room with a single small window it makes little difference.
Should I buy a 5-gallon bucket or individual gallons?
Buckets are cheaper per gallon and guarantee color consistency, but only if you will use most of it. Leftover paint in an opened bucket does not keep as well as sealed gallon cans.
Related calculators
- Drywall calculator: A 4×8 sheet is 32 sq ft, a 4×12 is 48
- Flooring calculator: Laminate, vinyl plank and hardwood
- Siding calculator: Courses = wall height ÷ exposure
Or start from all 22 calculators.