Paint Guide · 2 min read
How much paint for a 15×20 room?
A 15×20 room with 8-ft walls, one door and two windows needs 3 gallons for two coats — 509 sq ft of paintable wall at 350 sq ft per gallon.
A 15×20 great room is where the numbers get serious: roughly 500 sq ft of paintable wall on eight-foot ceilings and closer to 600 on nine-foot. Two coats need 3–4 gallons, and this is the size at which a five-gallon bucket is cheaper per gallon and easier to keep consistent.
Gallons by ceiling height and coats
One door and two windows deducted; 350 sq ft per gallon on smooth walls; rounded up to whole gallons.
| Ceiling | 1 coat | 2 coats | 3 coats | Wall area |
|---|---|---|---|---|
| 8 ft | 2 | 3 | 5 | 509 sq ft |
| 9 ft | 2 | 4 | 5 | 579 sq ft |
| 10 ft | 2 | 4 | 6 | 649 sq ft |
Don't forget
Primer. Going light over dark, or painting new drywall, add 2 gallons of primer. Ceiling. A flat ceiling paint for this room is 1 gallon at one coat. Texture. Orange-peel walls use about 10% more paint, knockdown about 20%; the planner adjusts for it.
This is also the size at which most people start pricing a painter. The planner shows a pro range next to the DIY number; for a room this big the gap is usually $1,000 or more, which is the real decision.
Other room sizes
10×10 room · 10×12 room · 12×12 room · 12×14 room · 14×16 room · 15×20 room
Last updated 2026-09-03. Method: how we calculate.