Finishes
Paint calculator
This calculator works out how many litres of paint a room or a set of walls needs, then turns that into the tins to buy. Enter the room size, or a wall area you already know, take off the doors and windows, and choose the number of coats.
What you need
This calculator works out the figures in your browser, which needs JavaScript switched on. The method below shows how to work it out by hand.
Estimates for planning and budgeting. Real quantities depend on the site and the workmanship, so check with your builder before you order.
Coverage depends on the paint and the surface. A good acrylic or PVA covers about 8 to 10 m² per litre per coat on smooth, primed walls; rough plaster and face brick drink much more. New plaster or skim should be primed or sealed first, which this calculator can include as a separate coat.
The tin count mixes 20, 5 and 1 litre tins to land as close as possible to what you need without running short.
How it is worked out
- Area = perimeter × height, plus the ceiling if chosen, less doors and windows.
- Litres = area × coats ÷ coverage per litre, and the same for the primer.
- Tins: as many 20 L as fit, then 5 L, then 1 L, rounding up the last one.
What it assumes
- Trims, doors and window frames are not included.
Common questions
How much paint for a 4 by 4 metre room?
Walls 2.7 m high give about 40 m² after a door and a window. At 8 m² per litre and two coats, that is about 10 litres, so two 5 litre tins.
Do I need to prime new plaster?
Yes. New plaster and skim are very absorbent; a primer or sealer stops the finish coat soaking in unevenly and saves paint.
How long between coats?
Most water-based wall paints can be recoated after two to four hours in warm weather. Check the tin.
Want exact quantities for your plan?
A calculator works one wall or one slab at a time. A bill of quantities works from your actual drawings and counts everything, which is what builders price against and what stops you buying twice.