Painting & Walls
Paint Calculator
Enter your room dimensions in metres to get the litres of paint and the number of cans to buy, with standard door and window deductions and an optional GST-aware cost estimate.
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.
Litres = total area ÷ coverage per litre. Typical Australian interior paint covers around 10–12 m² per litre per coat (default 11) — check your can. The result is rounded up to whole cans; set the container size to what you're 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.
- Paint needed: 86.6 ÷ 11 m²/L = 7.87 litres.
- With the container size set to a 4 L can: 7.87 ÷ 4 = 1.97 → round up to 2 cans.
Buy 2 × 4 L cans. At an example GST-inclusive price of $95 per can, that's $190.00 — Australian retail prices normally already include 10% GST.
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 and trims take gloss or semi-gloss enamel — calculate those separately from the wall paint.
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 ceilings, which take a flat ceiling paint with its own rate.
- 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:
- 2026-07-16
- Formula version:
- 1.0.0
- 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.
- Paint volume = total area ÷ the coverage rate you enter. The number of containers is the paint volume divided by your container size, rounded UP to the next whole container, because paint is sold in whole cans.
- The cost estimate multiplies the container count by the price you enter, then applies the tax rate you enter. 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 material estimate for planning purposes only. It is not a quotation, and it does not assess surface condition, primer requirements or colour-change coverage. Confirm quantities and the coverage rate on your specific product with your paint supplier before buying.