How to Calculate Interior Wall Paint Requirements
The standard coverage rate for premium Australian interior topcoat paint (Dulux, Taubmans and similar) is 16m² per litre per coat — confirmed directly against Dulux's own published paint calculator methodology. This assumes two coats for a standard repaint.
When You Need Primer
New or bare plasterboard, or a major colour change (like painting over a dark colour with white), needs a dedicated primer coat first. Primer has a different coverage rate to topcoat — approximately 14m² per litre, applied as a single coat before your regular topcoats.
Subtracting Openings
A standard Australian interior door averages roughly 2m² of surface footprint (2.04m × 0.82m), while a standard window accounts for approximately 1.5–2m². Subtracting these from your gross wall area avoids buying paint for surfaces that will never be painted.
Frequently Asked Questions
Add up the combined length of all the walls you're painting, enter the wall height, and subtract the number of doors and windows — the calculator handles the area maths and coverage rate for you, then shows the cheapest combination of tin sizes to actually buy for that amount.
The standard coverage rate for premium Australian interior topcoat paint is around 16m² per litre per coat, confirmed against major brands' own published methodology. Two coats is standard for a repaint, so a typical wall needs roughly one litre per 8m² once both coats are accounted for.
It checks combinations of 1L, 4L, 10L and 15L tins to find the cheapest way to cover your total litres needed, rather than just defaulting to the largest tin. Sometimes a 10L plus a 1L works out cheaper than a single 15L, depending on your specific pricing.
For a straightforward repaint over an existing coat in similar or lighter colour, no — go straight to topcoat. For bare plasterboard, very porous surfaces, or a big colour change (especially going from dark to light), primer significantly improves coverage and final colour accuracy.
To account for spillage, tray/roller loss, and cutting-in wastage around edges and corners — a standard allowance so you don't come up short near the end of the job.
Yes, ceiling paint typically shares the same approximate 16m²/L coverage as wall topcoat, so you can use this calculator for a ceiling by entering its length and width as your "wall length" and "height" figures instead.