Paint + Primer Coverage Calculator Australia — Litres & Leftover
Painting a room? This free paint and primer coverage calculator helps Australian DIYers and builders work out exactly how many litres of paint and primer a room needs — and unlike other calculators, we show you exactly how much paint you'll have left over for future touch-ups. Enter your room dimensions or wall area directly, choose your surface type, number of coats, and paint tier, and get an instant breakdown in metres and Australian dollars, sized to the 10L/4L/1L cans stocked by Bunnings. Results update live and include a full cost breakdown, so there are no surprises at checkout.
How to use this calculator
1. Measure your room or enter wall area directly
Get the length and width of the room in metres, plus the ceiling height — 2.4m is the default for most Australian homes, but adjust it for raked or higher ceilings. Prefer to skip the geometry? Switch to the "By wall area" tab and enter your total area in square metres directly. Toggle "Paint ceiling too?" on if you're covering the ceiling in the same colour, since that adds real area on top of your wall total.
2. Choose your surface type and number of coats
Pick the surface that matches your walls: bare drywall, previously painted, textured, or masonry. This matters — bare plasterboard soaks up noticeably more paint than a smooth, previously painted wall, because the raw board and set compound are porous. Then set your number of coats. Two coats is the default and the right call for most repaints. Drop to one coat only for a very close colour match on a wall already in good nick; bump to three over a dark colour or bare masonry.
3. Pick a paint tier and primer option
Choose economy, mid, or premium paint — this changes both the price per litre and the coverage rate, since better paint carries more solids and spreads further. Leave "Include primer?" on Auto and the calculator recommends primer for bare drywall automatically, skipping it for previously painted walls in good condition. If you're covering a dark colour with something much lighter, force primer on regardless of surface — one coat of undercoat saves you a second or third topcoat.
4. Review your paint, primer, and leftover estimate
Results update live as you type. You'll see your paintable area after doors and windows are subtracted, the litres needed for your chosen coats, and how many litres to buy — rounded up to the nearest combination of 10L, 4L, and 1L cans, matching what Bunnings actually stocks. Below that is our leftover box: how much paint you'll have left after the job, in litres and in square metres of future touch-up coverage — the figure most calculators leave out entirely.
The formula we use
Here's the exact math, start to finish. First we work out your wall area: perimeter × height, using 2 × (length + width) × ceiling height, in metres. Painting the ceiling too adds length × width on top. Next we subtract openings — 1.86 sqm per door and 1.39 sqm per window, standard sizes for a residential interior door and window — to get your paintable area.
From there: paintable area ÷ coverage rate = litres per coat, multiplied by your number of coats. We derive our metric coverage rates from the same base matrix used across every region — previously painted drywall at mid-tier works out to 9.8 sqm per litre, bare drywall at the same tier to 7.35 sqm per litre. Dulux and Taubmans tins often quote higher figures — up to 16 sqm per litre — measured on smooth, primed surfaces in ideal conditions. Australian interiors, especially older fibro or textured render, rarely match that, so our numbers stay conservative on purpose.
Finally, we round up to the smallest combination of 10L, 4L, and 1L cans that covers your need. Bunnings' can sizes are genuinely different from the UK's 5L/2.5L/1L lineup — this calculator uses AU-specific sizes, not a copy-pasted UK matrix.
A worked example
Let's walk through a real bedroom: 3.7m × 3.7m, 2.4m ceilings, previously painted walls, one door, two windows, mid-tier paint, two coats.
Wall perimeter: 2 × (3.7 + 3.7) = 14.8m. Wall area: 14.8 × 2.4 = 35.52 sqm. Subtract openings: 1 door (1.86 sqm) + 2 windows (2.78 sqm) = 4.64 sqm. That leaves 30.9 sqm of paintable area.
Previously painted drywall at mid-tier covers 9.8 sqm per litre, so one coat needs 30.9 ÷ 9.8 = 3.15 litres. Two coats: 6.3 litres. Rounded up to the smallest covering combination of cans, that's 7 litres — a 4L can plus three 1L cans of Taubmans Endure Interior at A$70 per 4L works out to A$122.50, which we round to A$123.
Those 7 litres leave roughly 0.7 litres spare after two coats — enough for a decent stretch of touch-ups on scuffed skirting or a nail hole, without opening a fresh can. Previously painted walls in good condition don't need primer, so A$123 is your full paint cost for the room. If this were bare plasterboard instead, you'd add a primer coat at the same 4L Bunnings can sizes, on top of that figure.
Regional cost context
Australian paint prices sit noticeably higher than the UK or US once you convert to a common unit — a well-known quirk of the local market that shows up clearly once you compare tiers.
Estimates are indicative only. As an Amazon Associate we earn from qualifying purchases. Retaining walls over 1 m and decks above certain thresholds may require council approval and/or an engineer (Form 15/16 in QLD). Verify with your local council before starting work.
| Product | Tier | Price | Container |
|---|---|---|---|
| Economy | Economy | A$31.5 | 4L |
| Mid | Mid | A$70 | 4L |
| Premium | Premium | A$131 | 4L |
| Primer | British Paints 4-in-1 Primer | A$78.5 | 4L |
Prices from Bunnings, current as of our last check — see our Methodology page for sources and verification dates.
Spring Low Sheen, a Bunnings own-brand line, at A$31.50 for 4L is the budget pick for ceilings, sheds, or rentals. Taubmans Endure Interior at A$70 for 4L is the mid-tier standard for most lived-in rooms — solid coverage and a wipeable finish without specialty pricing. Dulux Wash&Wear +PLUS Kitchen & Bathroom at A$131 for 4L sits at the premium end, built for moisture and mould resistance in bathrooms and kitchens specifically, not just a nicer finish on a bedroom wall.
British Paints 4-in-1 Primer, at A$78.50 for 4L, costs more per litre than even the premium topcoat above — Australian paint carries a real premium tier spread, roughly 4x between economy and premium, wider than either the UK or US market. All figures reflect our last direct Bunnings check (see Methodology); expect some price variation between stores and states.
Shop on Amazon: Zinsser Bulls Eye 1-2-3 primer
A quick safety note: lead paint
Homes built before 1970 are the highest risk for lead-based paint in Australia, since lead content in domestic paints was progressively restricted through the 1970s and fully phased out by the late 1990s. If you're sanding, scraping, or demolishing painted surfaces in an older home, test first — a lead test kit from a hardware store is a cheap first check — and follow safe work practices around dust. Safe Work Australia and your state health department both publish current guidance if you're unsure.
Common mistakes to avoid
- Skipping primer on bare plasterboard. New board soaks up paint unevenly without it, leaving patchy sheen once the topcoat dries. Prime first on anything unpainted.
- Forgetting to subtract doors and windows. A room with two windows and one door has nearly 4.6 sqm less wall than raw perimeter × height suggests — skip that step and your leftover number will be off too.
- Assuming UK or US can sizes apply here. Bunnings stocks 10L, 4L, and 1L — not the UK's 5L or the US's 1-gallon cans. Always check this calculator's regional result rather than a memory of a can size from overseas.
- Rounding down "to save a trip." If the maths says 6.3 litres, buy the covering combination shown — running dry halfway across a wall on a 35°C day is a worse afternoon than grabbing one extra litre tin.
- Treating render or brick like plasterboard. Masonry surfaces are far more porous. Pick "Masonry/brick" as your surface type or you'll run short on a rendered exterior or feature wall.
- Planning a bigger project? If you're also building a deck, see how many boards you'll need with our composite decking calculator. Adding a retaining wall to the yard too? Check our retaining wall block calculator for besser blocks and gravel.
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Frequently asked questions
How much paint do I need for a room?
A typical 3.7m × 3.7m bedroom with 2.4m ceilings needs about 7 litres for two coats on previously painted walls — a 4L can plus a couple of 1L top-ups, matching Bunnings' 10L/4L/1L can sizes. Bare plasterboard or a dramatic colour change will need more, plus a primer coat. Use the calculator above with your exact room dimensions, surface type, and number of coats for a precise litre and cost estimate rather than a rule of thumb.
How many litres of paint per square metre?
It's usually expressed the other way around — square metres per litre — and it depends on surface and tier. Previously painted walls cover roughly 8.6-11 m² per litre; bare plasterboard covers less, around 6.1-8.6 m² per litre, since raw board soaks up more paint. Flip that around and you're using roughly 0.09-0.16 litres per m², depending on tier and surface. Our conservative figures sit below what Dulux or Taubmans print on the tin, on purpose.
Do I need a primer or undercoat?
Bare plasterboard always needs a primer or undercoat — it seals the porous board so your topcoat goes on evenly instead of soaking in patchy. Previously painted walls in good condition usually don't, unless you're covering a dark colour with something much lighter, where undercoat saves you a second or third topcoat. Our calculator recommends primer automatically based on surface type, and you can override it to "Always include" for a big colour change.
How much paint for two coats?
For a 3.7m × 3.7m room with previously painted walls, two coats of mid-tier paint need 6.3 litres — rounded up to 7 litres once you factor in real Bunnings can sizes (a 4L can plus 1L top-ups). One coat alone needs about 3.15 litres for the same room. Two coats is standard for most repaints; bare plasterboard or a dark-to-light change may need a third coat plus a primer layer first.
How much paint for a ceiling?
Ceilings use the same coverage math as walls — just swap in your ceiling's area (length × width) instead of wall area, and there's no need to subtract doors or windows. Toggle "Paint ceiling too?" on in the calculator above if you're doing both in the same session, and it adds your ceiling area straight into the total automatically. Ceilings are usually flat, previously-painted drywall, so they typically use the same tier and coverage rate as your walls.
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Estimates are indicative only. As an Amazon Associate we earn from qualifying purchases. Retaining walls over 1 m and decks above certain thresholds may require council approval and/or an engineer (Form 15/16 in QLD). Verify with your local council before starting work.
Last updated: August 2026. Estimates are for planning purposes only. Verify with local suppliers before purchase. Coverage rates are generic averages; actual coverage varies by product, application method, and surface condition — check your specific paint can's label before buying.