Paint calculator
Enter the room’s size and count the doors and windows. The calculator takes them out of the wall area for you.
Paint needed
1.91 gallons
- Cans to buy
- 2 1-gallon cans
- Paintable area
- 334 sq ft per coat
How it works
Wall area is the room’s perimeter (2 × length + 2 × width) times the wall height. The calculator subtracts about 20 square feet per door and 15 per window, adds the ceiling if you’re painting it, multiplies by the number of coats, and divides by the coverage on the can.
Coverage on the label assumes smooth, primed walls. Rough texture, fresh drywall and bare wood soak up more, so expect less coverage on those.
Example
With room length 12 ft, room width 12 ft, wall height 8 ft, doors 1, windows 2, coats 2, coverage per gallon 350 sq ft, paint the ceiling too: no, walls only, the answer is 1.91 gallons.
Tips before you buy
- Changing to a very different color usually takes two coats, or a primer coat plus one or two finish coats.
- Five-gallon buckets cost less per gallon. They make sense once you need four or more gallons of one color.
- Keep a little leftover paint, labeled with the room and color, for touch-ups.
- Ceilings are usually painted with a flat ceiling paint, not the wall color. Run it separately if so.
Common questions
How much paint do I need for a 12×12 room?
With 8-foot walls, one door and two windows, about 2 gallons covers two coats on the walls.
How many square feet does a gallon of paint cover?
Most interior paints list 350–400 square feet per gallon for one coat on a smooth, primed surface.
Do I need two coats of paint?
Usually, yes. Two coats give even color and better durability, especially when covering a different color.