Paint Calculator
Enter your room measurements and we will work out how much paint to buy. The calculator assumes standard Australian door and window sizes, applies your chosen number of coats, and recommends sensible tin sizes.
Enter your measurements
Your litres of paint result will appear here instantly.
How to use this calculator
- 1
Measure the length and width of the room, and the height of the walls, in metres or centimetres.
- 2
Count the doors and windows in the room — we subtract standard sizes for you (0.9 × 2.1 m door, 1.2 × 1.2 m window).
- 3
Leave coats at 2 unless you are painting over a dark colour or bare plasterboard, which often needs 3.
- 4
Check your paint tin for its coverage figure (m² per litre per coat) and adjust the coverage field if it differs from the default of 10.
- 5
Buy the nearest larger tin size to your result — or a combination of tins — rather than trying to buy the exact amount.
How the calculation works
Wall area
We calculate the perimeter of the room (2 × length + 2 × width) and multiply it by the wall height to get the total wall area.
Doors and windows
Each standard door subtracts 1.89 m² and each standard window subtracts 1.44 m² from the paintable area. Measure large feature windows or double doors yourself and adjust.
Paint required
Paintable area ÷ coverage (m² per litre) × number of coats = litres required. We round up slightly to the nearest practical amount.
Worked example
A bedroom measuring 4 m × 3 m with 2.4 m ceilings, one door, one window and 2 coats.
Wall area = 2 × (4 + 3) × 2.4 = 33.6 m². Minus door (1.89 m²) and window (1.44 m²) = 30.27 m² paintable.
30.27 m² ÷ 10 m²/L per coat × 2 coats = 6.1 litres.
You need approximately 6 litres of paint — buy one 4 L tin plus one 2 L tin, or a single 6–10 L tin if your brand sells one.
Frequently asked questions
How much wall does one litre of paint cover?
Most interior acrylic paints sold in Australia cover roughly 10–16 m² per litre per coat, depending on the brand, surface texture and porosity. The default of 10 m²/L here is deliberately conservative. Check the coverage stated on your tin and adjust the field.
How many coats should I plan for?
Two coats is the standard for repainting walls in a similar colour. Plan three coats when painting white over a dark colour, over new plasterboard, or when using a dramatically different colour. Good preparation and quality rollers rarely change the coat count, but poor preparation always does.
Does this include the ceiling?
Only if you tick the ceiling option. Ceilings are usually painted with a dedicated ceiling paint (flat white, high hiding) and are calculated separately from walls. If you include it here, remember the coats and coverage for ceiling paint often differ from wall paint.
Should I buy exactly the calculated amount?
No. Buy slightly more than calculated — you will use extra on cutting in, minor spills and touch-ups later. Leftover sealed paint is handy for wall repairs, but if you overbuy significantly, most unopened tins can be returned or donated.
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Results are estimates only. Always confirm material requirements with your supplier or a qualified professional before purchasing.