Free tool
Paint quantity calculator
Estimate how many litres of paint you need for a wall or ceiling, by area and number of coats.
How it works
We multiply your area by the number of coats and divide by the paint coverage per litre. Coverage varies by paint and surface, so check the figure printed on your paint tin before buying.
How the calculation works
Litres needed is your paintable area multiplied by the number of coats, divided by the coverage of the paint. Coverage is the number that actually decides your answer, and it is printed on the tin: interior emulsion typically covers 100 to 140 sq ft per litre per coat on a smooth, puttied surface. The tool defaults to 120 and also shows a separate figure for one coat of primer.
Working out the paintable area
This is where most estimates go wrong, because people use floor area. For walls, take the room perimeter and multiply by the wall height, then subtract the doors and windows. A 12 by 12 ft room with 10 ft walls has a perimeter of 48 ft, so 480 sq ft of wall, less perhaps 60 sq ft for a door and a window, giving about 420 sq ft. Add the ceiling separately if you are painting it, which is simply the floor area.
As a rough sanity check on a whole house, paintable internal area often lands somewhere around three to four times the built-up area once every wall and ceiling is counted. Use it to check your figure is in the right region, not as the figure itself.
New walls need more than paint
| Situation | Typical system |
|---|---|
| New plaster, first time painting | Wall putty to smooth the surface, then primer, then two coats of emulsion |
| Repainting a sound wall | Cleaning and patching, then one to two coats. Primer usually not needed |
| Repainting a damaged or damp wall | Fix the cause first. Paint over damp and it will fail again within a season |
| External walls | Exterior-grade paint, which covers less per litre and needs two coats |
Putty is not paint and is not included in this estimate. On new plaster it is a significant separate cost, and it is also what determines whether the finished wall looks flat and even, so it is a poor place to economise.
Why your painter may ask for more
Deep or saturated colours often need an extra coat to look even, because the pigment does not hide the surface as well. Rough or highly absorbent plaster drinks the first coat. Spray application uses more than a roller. And covering a dark existing colour with a pale one can take three coats. None of these mean you were overcharged; they mean coverage is a property of the job, not just of the tin.
Frequently asked questions
Do I really need primer?
On new plaster or putty, yes. Primer seals a porous surface so the emulsion sits on top instead of soaking in, which means better colour, better coverage and a longer life. On a sound previously painted wall you can usually skip it.
How many coats should I budget for?
Two is the standard assumption and the tool defaults to it. Budget for three if you are using a strong colour, going pale over dark, or painting an absorbent new surface.
Does this cover putty, labour or exterior paint?
No. This is paint quantity only. Putty, primer beyond the single coat shown, labour, scaffolding and the higher consumption of exterior grades are all separate. For a whole-house view of where paint sits in the budget, see our budget split guide.