Paint Calculator
🇦🇺 Australia version
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.
Use Paint Calculator online
Paint Calculator
Work out how much paint a job really needs — walls, ceilings and trim, adjusted for texture, colour change and the number of coats — then turn it into a shopping list.
Area to cover, by room
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) (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.
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
- 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.
- Choose the surfaces. Leave walls and ceiling ticked and untick the woodwork box when you are only repainting the big surfaces.
- 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.
- Adjust coats and primer. Raise the coats if you cover a dark colour, and turn on primer when going over raw sheeting.
- 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.
- When you need to convert gallons, litres or square measures, use the Unit Converter.
- 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.