Painting & Walls
Wall and Ceiling Paint Calculator Australia
Enter room dimensions in metres to get separate two-coat takeoffs for wall and ceiling paint. Wall openings are deducted, the ceiling uses length × width, and each finish has editable coverage, can size, and price.
Formula tested · Local units · No sign-up
Project inputs
Enter measurements
Use your preferred units. Results update automatically.
Show the calculation methodFormula, conversions, rounding, and assumptions+
Wall area = 2 × (room length + room width) × wall height. A 6 m × 4 m room with 2.4 m ceilings has 2 × 10 × 2.4 = 48 m² of wall. You can also enter a measured wall area directly.
Standard openings are deducted: 1.9 m² per door and 1.4 m² per window (editable typical values). The remaining paintable area is multiplied by the number of coats — two coats is standard for interior low-sheen.
Ceiling area = room length × room width and is multiplied by its separate coat count. Direct wall-area mode requires a separate ceiling area when the ceiling is included.
Litres = coat-area ÷ the coverage per litre printed on that product. Wall and ceiling can counts are rounded separately; set each container size to what you are buying, such as the common 4 L can.
Real-world example
Worked example: 6 m × 4 m lounge, 2.4 m ceilings, 2 coats
- Wall area: 2 × (6 + 4) × 2.4 = 48 m².
- Deduct openings: 1 door (1.9 m²) + 2 windows (2 × 1.4 m²) = 4.7 m² → 43.3 m² paintable.
- Two coats: 43.3 × 2 = 86.6 m² to cover.
- Wall paint: 86.6 ÷ 11 m²/L = 7.87 litres → 2 × 4 L cans.
- Ceiling: 6 × 4 = 24 m²; two coats = 48 m²; 48 ÷ 11 = 4.36 litres → 2 × 4 L ceiling-paint cans.
Buy 2 × 4 L wall-paint cans and 2 × 4 L ceiling-paint cans. Enter separate prices for the two finishes; if you enter GST-inclusive retail prices, leave the additional tax field at zero.
Before you start
How to measure
- Measure the room's length and width in metres, and the wall height from floor to ceiling — 2.4 m is the common Australian ceiling height, with 2.7 m in many newer homes.
- Count doors and windows; the calculator subtracts standard areas (1.9 m² per door, 1.4 m² per window). Measure sliding doors and full-height windows separately.
- Ceilings usually take a dedicated flat ceiling paint, so use the ceiling coverage and can size printed on that product; trims still need a separate gloss or semi-gloss estimate.
Local guidance
Notes for Australia
- Australian interior wall paint is commonly sold in low-sheen or matt acrylic, in 1 L, 2 L, 4 L, 10 L and 15 L cans — the 4 L can is the standard retail size.
- Coverage on Australian labels is quoted in m² per litre, typically 10–12 for low-sheen acrylic on a previously painted surface; new plasterboard needs a sealer/undercoat first.
- GST is 10% and advertised retail prices normally include it; trade accounts often see ex-GST pricing — check before comparing quotes.
Quick reference
Typical coverage by surface (planning values — check your can)
| Surface | Typical coverage per coat |
|---|---|
| Previously painted plasterboard | 11–12 m²/L |
| New plasterboard (after sealer) | 10–11 m²/L |
| Textured render | 6–9 m²/L |
| Bare brick or masonry | 5–8 m²/L |
Editable planning values only — the coverage figure on your can governs.
Good to know
Common mistakes to avoid
- Skipping the sealer/undercoat on new plasterboard — topcoat coverage and finish both suffer.
- Using wall-paint coverage figures for flat ceiling paint without checking its own label — the calculator provides separate settings for both.
- Assuming one coat of low-sheen will cover a strong colour change — two coats is the norm, more over dark colours.
- Comparing a trade ex-GST quote against a GST-inclusive retail price as if they were the same.
Need help?
Frequently asked questions
How many square metres does a 4 L can cover?
At a typical 11 m² per litre, a 4 L can covers about 44 m² in one coat — roughly 22 m² of wall at two coats. Check your can: coverage varies by brand and sheen level.
One coat or two?
Two coats is the standard for interior low-sheen and is what this calculator defaults to. A similar colour over a sound existing finish can sometimes get away with one; strong colour changes may need more.
Is GST included in the cost estimate?
Only if you include it. Australian retail shelf prices normally already include 10% GST, so enter the shelf price and leave tax at 0 — or enter an ex-GST trade price and 10% tax and the calculator adds it.
Keep planning
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About this calculator
- Written by:
- BuildMeasure Editorial Team
- Technically reviewed by:
- Pending independent technical reviewer (formula unit-tested; see methodology)
- Last reviewed:
- 2026-07-20
- Formula version:
- 1.1.0
- Region reviewed for:
- Australia
- Spotted an error?
- Report a correction
Methodology
- Wall area comes either from room dimensions (perimeter × wall height, i.e. 2 × (length + width) × height) or from a directly entered area. All arithmetic runs internally in SI units (m² and litres) to avoid unit drift; regional units are converted on the way in and out.
- Standard opening deductions (door and window areas, clearly labelled next to the inputs and editable via the counts) are subtracted from the wall area, floored at zero. The paintable area is multiplied by the number of coats to get the total area to cover.
- When the ceiling is included, room mode calculates its area as length × width; direct-area mode uses the ceiling area you enter. Ceiling coats, coverage, container size, and price stay separate from the wall product so the tool never silently treats two finishes as interchangeable.
- Paint volume = coat-area ÷ the coverage rate you enter. Wall and ceiling container counts are each rounded UP to the next whole container, because separate paint products cannot share a partly used can in the estimate.
- The cost estimate multiplies each container count by the matching price you enter, then applies the tax rate only when every included product has a price. No prices are built in.
- The formula is covered by automated unit tests, including hand-calculated worked examples, and is versioned (see formula version on this page).
Sources & standards
- Unit definitions: Metric units throughout; common Australian can sizes are 1 L, 2 L, 4 L, 10 L and 15 L.
- Coverage defaults: 10–12 m² per litre per coat is a typical low-sheen acrylic label range; the figure on your can governs.
This tool provides a wall-and-ceiling paint material estimate for planning purposes only. It is not a quotation, and it does not assess surface condition, primer requirements, trim paint or colour-change coverage. Confirm quantities and each product's coverage rate with your paint supplier before buying.