--- title: "Paint Calculator for Australia: Litres by Room in Metres | AumnI tools" description: "Estimate litres of wall and ceiling paint for each Australian room from metres, doors, windows, coats and wall texture, rounded up to whole 2.5 litre cans." url: https://aumnitools.com/au/tool/paint-calculator category: "Lifestyle" country: "Australia" updated: 2026-11-08 --- # Paint Calculator Painting an Australian home usually starts with a tape measure in metres and ends with a trip to the hardware store for cans. This version works in metres and litres, starts at 12 square metres per litre as a typical figure, and rounds up to whole 2.5 litre cans per product so you buy enough. ## Australia rules and figures - Australian floor and wall areas are quoted in square metres, so the page starts in metres, litres and square metres per litre. - Wall paint starts at 12 m² per litre, a spread rate typical of manufacturers rather than any official standard; match it to the can you buy. - No can price is filled in; type the shelf price, which already includes GST at 10%. - Cans start at 2.5 litres, which you can change for the pack sizes your store stocks. Sources: [ATO: Australian Taxation Office (GST rate)](https://www.ato.gov.au) (checked 2026-11-08) ## How the Paint Calculator works The tool multiplies each room’s perimeter by its height, removes a standard door and window per count, then divides the area by an effective spread rate. That rate falls when the surface is rough or the colour change is large. Formula: `litres = (m² × coats) ÷ (m² per litre ÷ texture ÷ colour); cans = litres ÷ can size, rounded up` - Each door takes off 0.81 × 2.03 m and each window 0.9 × 1.2 m. Ceilings count the full floor area with no deduction. - Wall and ceiling paint begin at 12 m² per litre, and trim and primer at about 10.3 m². Replace either with the rate printed on your can. - Surface choices multiply paint absorbed: 1.1 for light texture, 1.25 heavy, 1.4 bare plaster or new plasterboard and 1.6 for brick or render. - Cans start at 2.5 litres with the price empty, so enter what a can costs including GST. ## How to use the Paint Calculator 1. **Enter the room.** Give the room a length, width and height in metres and count its doors and windows. Use Add room for each extra space. 2. **Choose the surfaces.** Leave walls and ceiling ticked and untick the woodwork box when you are only repainting the big surfaces. 3. **Pick the wall type.** Open Paint needed and set Surface being painted to match, from smooth old paint to new plasterboard that soaks paint up. 4. **Adjust coats and primer.** Raise the coats if you cover a dark colour, and turn on primer when going over raw sheeting. 5. **Total the order.** Enter the price of a can, then read litres and cans. Export CSV saves it for the store visit. ## Example: A 4.2 × 3.6 × 2.7 m bedroom on new plasterboard The room has 42.12 m² of gross wall. With 1 door and 2 windows removed, 38.32 m² of wall remains, plus 15.12 m² of ceiling. New plasterboard is set to bare plaster, a factor of 1.4, so wall paint spreads at 7.29 m² per litre after the default colour uplift. Two coats take 10.50 litres, or 5 cans of 2.5 litres. The ceiling takes 3.53 litres at 8.57 m² per litre, which is 2 cans. ## When to use the Paint Calculator - **New-build plasterboard.** Choose the bare plaster setting and switch on primer to cover the sealer coat and the two top coats. - **Rental repaint.** Add each room, tick only the walls, and price the cans before an end-of-lease clean-up. - **Ceilings only.** Untick walls and woodwork to see how many cans a bedroom ceiling needs after water staining. - **Dark to light change.** Raise the colour slider to estimate the extra litres when covering a dark feature wall. ## What the Paint Calculator does not do - The starting spread rates are typical manufacturer figures, not an official standard, so a tin that states a different rate needs that figure typed into the spread-rate box. Other countries start with litres and no price, which you enter. - Doors and windows use one standard size each, so a patio door or a large picture window is under- or over-deducted. - Rooms are rectangles with flat ceilings and no alcoves, stairs, gables or radiators. - The texture and colour factors are rules of thumb, not a paint maker's data. Check the spread rate printed on your tin. - Nothing is saved: the rooms reset to the two examples when you reload. ## When something else is a better fit - **When you want floor area, perimeter and a boxes-of-material order for flooring**, use the [Room Measurement Calculator](https://aumnitools.com/tool/room-measurement-calculator.md). - **When you need to convert gallons, litres or square measures**, use the [Unit Converter](https://aumnitools.com/tool/unit-converter.md). - **When the surface is exterior brick, a ceiling with beams or a spray job**, use the paint manufacturer's own calculator or a trade quote. ## Questions about the Paint Calculator ### How much paint does a 4.2 by 3.6 metre bedroom need? With a 2.7 m ceiling, 1 door and 2 windows, it needs 10.50 litres for the walls and 3.53 for the ceiling on new plasterboard at two coats. Smooth old paint needs less because its factor is 1. ### What does the bare plaster setting do? It multiplies the paint absorbed by 1.4, so the spread rate falls from 12 to about 8.6 m² per litre before the colour factor. New plasterboard and fresh plaster soak up the first coat quickly. ### Why are the cans rounded up? You cannot buy part of a can. Each product rounds separately, so 3.2 litres of ceiling paint becomes 2 cans of 2.5 litres even though the second is mostly spare. ### Is the 12 m² per litre figure official? No. It is a typical manufacturer figure, and individual paints state their own. Type the rate from the can into the spread-rate box for each product and the totals follow it. ### Does the price include GST? Only if the price you type does. Australian shelf prices include 10% GST, so entering the price printed on the shelf gives the real cost of the cans, with nothing to add. ## Related tools - [Room Measurement Calculator](https://aumnitools.com/tool/room-measurement-calculator.md): Floor, wall and volume totals for several rooms, in feet or metres - [Unit Converter](https://aumnitools.com/tool/unit-converter.md): Converts 102 units in 11 categories, with temperature offsets and 0 to 12 decimals - [Home Maintenance Reminder](https://aumnitools.com/tool/home-maintenance-reminder.md): 45 home jobs with set intervals; log last-done dates to see what is overdue ## About this page Runs in your browser: what you enter is processed on this device and is not uploaded. Last checked against the tool's code on 2026-11-08. Interactive version: https://aumnitools.com/au/tool/paint-calculator