How it works
Tell the calculator the size of the room and how many coats you're doing — it handles the doors, windows and coverage math.
Enter the room
Type length, width and ceiling height, or switch to wall area if you've already measured the walls.
Subtract openings
Add how many doors and windows to skip. We deduct standard sizes so you don't overbuy.
Get gallons
See how many gallons to buy for your chosen number of coats, rounded up to whole cans.
Estimating paint without the guesswork
Painting a room comes down to one number: the wall area you actually have to cover. For a rectangular room that's twice the length plus twice the width, multiplied by the ceiling height. A 12 × 12 room with 8-foot ceilings has 384 square feet of wall before you take anything out.
Then you subtract the parts you won't paint. A standard interior door is about 21 square feet and an average window about 15, so a room with one of each drops to roughly 348 square feet. Multiply by the number of coats, divide by how far a gallon goes, and you have your answer.
How far does a gallon really go?
Manufacturers quote around 350–400 square feet per gallon, and that holds on smooth, primed drywall. New drywall, textured surfaces and deep or dramatic color changes all drink more paint, which is why two coats is the sensible default and why we always round up to whole gallons — running out halfway through a wall is how you get visible lap marks.
Frequently asked questions
How much paint for a 12×12 room?
With 8-foot ceilings, one door and one window, a 12 × 12 room needs about 2 gallons for two coats.
How many square feet does a gallon cover?
About 350–400 square feet per coat on smooth walls. Rough or unprimed surfaces cover less.
Do I need one coat or two?
Two coats is standard. Use three for bold colors, light-over-dark changes, or fresh drywall.
Does this include the ceiling?
No — this estimates wall paint only. For a ceiling, use "Wall area" mode and enter length × width as the area.
More material calculators
Estimates are for planning only and assume standard door/window sizes and paint coverage. Check the coverage printed on your paint can before buying.