To calculate paint for a room, work out the wall area, subtract doors and windows, multiply by the number of coats and divide by the coverage printed on the tin. Here’s a worked example so you can see the numbers.
The example room
Say the room is 4 metres by 3 metres with a 2.4 metre ceiling, one door and one window.
Step 1: Wall area
The perimeter is 4 + 3 + 4 + 3 = 14 metres. Multiply by the ceiling height: 14 x 2.4 = 33.6 square metres.
Step 2: Subtract openings
A standard door is about 1.6 square metres and a window might be around 2 square metres. Together that’s roughly 4 square metres, leaving 29.6 square metres of wall.
Step 3: Multiply by coats
Two coats means 29.6 x 2 = 59.2 square metres of paint to cover.
Step 4: Divide by coverage
Check the tin. If it says a litre covers 12 square metres, then 59.2 divided by 12 comes to just under 5 litres. That figure is only an example, so use the coverage on your product. Round up to the next tin size so you don’t run short.
Step 5: Don’t forget the ceiling
The ceiling is 4 x 3 = 12 square metres. Two coats is 24 square metres, which at the same coverage needs about 2 litres. Ceilings often use a different paint, so buy it separately.
Step 6: Trims and doors
Skirtings, door frames and doors use a separate, smaller amount of gloss or semi-gloss paint. A litre usually goes a long way on a standard room’s trims.
Things that change the numbers
- Dark to light colour changes may need extra coats or a primer
- Rough or new plaster soaks up more paint
- Textured walls have more surface area than smooth ones
- Spraying uses more paint than rolling
Planning a bigger job?
Our guide to calculating how much paint you’ll need covers whole-project estimates. Before painting, see how to prep a wall for painting.
Numbers first, paint second
A few minutes with a tape measure saves a trip back to the shop. See our interior house painting service, or request a quote if you’d rather hand it over.
McAuliffe Painting. Eagle Farm, Brisbane QLD 4009. QBCC Lic 15183972.
