Wall length, height, doors, windows and coats in, litres and a 10L/4L/1L shopping list out. Built for the trip to the paint shop, free, no email.
4.6L of paint
32.4m² of wall, 2 coats at 14m² per litre.
Buy: 1 × 4L + 1 × 1L (5L total, rounded up so you do not run out mid-wall).
Guide only. Porous or patched surfaces drink more, dark-to-light colour changes need an extra coat, and spraying uses more than rolling. Check the actual coverage figure on your tin, most Australian acrylics sit around 14 to 16m² per litre.
Running out mid-wall is the expensive mistake. You stop with a wet edge, drive 25 minutes each way, and the batch you buy in a hurry may not tint identically to the first. That join line where coat one dried is visible forever. The calculator rounds the tin list up on purpose, a spare litre in the shed for touch-ups beats a visible lap mark in the hallway.
For painters quoting on the phone, the same sliders work in reverse. Walk the client through wall length and height while you talk, and the litres, and therefore the materials line on your quote, are done before the call ends.
A typical 4m x 4m Australian bedroom with 2.4m ceilings has about 38m² of wall once you take out a door and a window. At two coats and 14m² per litre, that is around 5.5 litres, so a 4L tin plus two 1L tins, or a 10L if you are doing more than one room in the same colour. Bigger rooms, higher ceilings and darker colour changes all push it up, which is exactly what the sliders above are for.
Almost always, yes. One coat over a similar colour on a well prepped wall can pass in good light, but it rarely covers evenly, and the patchiness shows up worst in the afternoon sun. Two coats is the standard for a reason. Going from a dark colour to a light one, or painting over fresh plaster, often means a primer or third coat, so bump the coats button and let the litres update.
Check the tin, it is printed on every one. Most Australian interior acrylics claim 14 to 16m² per litre on a sealed, smooth surface. Real-world coverage is usually a touch lower, porous or textured surfaces drink more, and spraying uses more than rolling. The calculator defaults to 14 as an honest middle. If your tin says 16 and your walls are in good shape, slide it up.
No. Ceilings normally take a dedicated flat ceiling paint, which hides roller marks and imperfections far better than wall paint does, and it is nearly always a different white anyway. When you toggle the ceiling on, treat those litres as a separate purchase. Same maths, separate tins.
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