Paint Calculator
Estimate how much paint you need for a room's walls (and ceiling) in gallons or litres, allowing for doors, windows and the number of coats.
How to use
- 1Enter the room's length, width and wall height.
- 2Enter the number of doors and windows and the coats you'll apply.
How it's calculated
Wall area = 2 × (length + width) × height − 21 ft² per door − 15 ft² per window. Paint = area × coats ÷ coverage (about 350–400 ft² per gallon, or 10 m² per litre).
Frequently asked questions
How many coats do I need?
Usually two. One may do when repainting a similar colour with good paint; dark-to-light changes can need a primer plus two coats.
How much does a gallon cover?
About 350–400 sq ft on smooth, primed walls — less on textured or porous surfaces.
Should I buy extra?
Keep a little for touch-ups; buying all the paint at once also avoids colour differences between batches.