Calculator
Paint Calculator
Enter the room or wall size. It gives litres of putty, primer and paint separately, since all three cover very differently.
The formula
Wall area = Perimeter x Height
Paintable area = Wall area - doors and windows
(+ ceiling if you include it)
Litres = Paintable area x number of coats / coverage
COVERAGE
Putty 25 sq ft per kg
Primer 130 sq ft per litre
Emulsion 110 to 140 sq ft per litre per coat
What this assumes
- Coverage figures are for a smooth, properly finished wall. Rough walls drink much more paint.
- Two coats of paint are assumed. Dark colours often need three.
- New walls need putty and primer. Repainting an old wall may not.
- Exterior paint covers less area and costs more per litre than interior.
- Coverage printed on the bucket is usually the best case. Real site coverage is 10 to 15% lower.
Common questions
How much paint for a 10 x 12 room?
Walls only, two coats, roughly 8 to 10 litres. Add the ceiling and it goes to about 12 litres. Putty and primer are extra.
Why does the shop say I need more paint than this?
Two reasons. Rough walls take more, and shops usually assume you will want extra in hand. Buy about 10% more than calculated, but not double.
Is putty always needed?
On new plaster, yes. It fills small holes and gives a smooth surface so the paint looks even and lasts longer. On a well maintained old wall you can skip it.
Interior or exterior paint for balcony walls?
Exterior. Anything that gets direct rain or sun needs exterior grade. It costs more but interior paint will peel within a year or two.