About this calculator
How much paint a room needs, split into wall and ceiling paint, with sensible can sizes so you don’t overbuy.
How it’s calculated
Paint = area × coats ÷ coverage. Typical coverage is 350–400 sq ft per gallon on smooth, primed drywall. Doors and windows are deducted at standard sizes.
Worked example
With these inputs:
- Room length
- 14 ft
- Room width
- 12 ft
- Wall height
- 8 ft
- Doors
- 1
- Windows
- 2
- Paint the ceiling
- Yes
- Coats
- 2
- Coverage (sq ft per gallon)
- 350
- Add a primer / mist coat
- No
the result is:
- Wall paint
- 2.09 gal
- Wall area (net)
- 366 sq ft
- Ceiling area
- 168 sq ft
- Primer
- 0 gal
Tips from the trade
- New plaster or drywall is thirsty: prime or mist-coat it first.
- Rough, textured or dark surfaces can drop coverage by 20–30%.
- Big colour changes (dark to light) usually need a third coat.
Common questions
How much paint for a 12×12 room?
With 8 ft walls and two coats, about 2 gallons for the walls and 1 for the ceiling.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.