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 3.78 L can 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 3.78 L can)
- 350
- Add a primer
- No
the result is:
- Wall paint
- 7.9 L
- Wall area (net)
- 366 sq ft
- Ceiling area
- 168 sq ft
- Primer
- 0 L
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 two 3.78 L cans for the walls and one for the ceiling.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the building code adopted in your province before ordering.