How much paint do I actually need?
The sum is simple, but two things trip people up: forgetting to take the doors and windows off, and using an American coverage rate.
Most Australian interior wall paints publish a spread rate of about 16 square metres per litre per coat on a prepared surface. A lot of the free calculators online default to 12 m²/L, which is a generic figure — use it on an Australian job and you'll order roughly a third more paint than you need. On a typical room that's an extra 4-litre tin sitting in the shed forever.
A worked example
A 4m × 3m room with 2.4m ceilings. The walls add up to 14 lineal metres, so:
- Gross wall area: 14 × 2.4 = 33.6 m²
- One door (0.82 × 2.04) and one window (1.2 × 1.2): −1.67 −1.44 = 30.5 m² to paint
- Two coats at 16 m²/L: 30.5 × 2 ÷ 16 = 3.8 litres
- Plus 8% for waste: 4.1 litres — so a 4L tin plus a 1L, or just a 10L if you've got more rooms coming
Coverage rates by paint type
| Product | Typical Australian coverage |
|---|---|
| Interior wall paint (low sheen, matt) | ~16 m² per litre |
| Ceiling paint | ~16 m² per litre |
| Primer / undercoat | ~12–14 m² per litre |
| Enamel trim paint | ~16 m² per litre |
| Exterior on render or masonry | ~10–12 m² per litre (porous surfaces drink it) |
These are starting points. The technical data sheet on the manufacturer's website is the real number for the product you're actually using, and it's worth thirty seconds to check — especially on a big job where the difference is a whole tin.
What eats more paint than you expect
- Bare or patched plasterboard — the first coat soaks in. Prime it, or budget an extra coat.
- Render, brick and besser — texture means more surface area than the flat measurement suggests. Ten to twelve square metres a litre is more realistic.
- Big colour changes — going light over dark, or covering a strong red or navy, is a three-coat job whatever the tin says.
- Spraying — faster, but overspray means more paint than rolling. Add 15–20%.
Buying the right tins
Paint isn't priced evenly. A 10L tin is usually much cheaper per litre than three 4L tins, so the cheapest way to buy 11 litres often isn't the obvious one. Put your tin prices into the calculator and it'll work out the cheapest combination that covers what you need, and tell you how much you'll have left over.
A litre or two spare is worth having for touch-ups — write the room and the colour code on the lid with a marker before it goes in the shed.
Quoting a paint job
Materials are the easy half. The part that decides whether a paint job makes money is prep: filling, sanding, taping, drop sheets and cutting in. On a repaint of an occupied house, prep can be more hours than painting.
Price the prep as its own line on the quote, so the customer can see what they're paying for and you have something to point at when they ask why it isn't just "paint and go".
Worked out the paint. Now price the job.
Yamate turns your materials and hours into a quote the customer can accept on their phone, then an invoice, then a payment — with GST handled and the follow-ups chased for you.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberPaint coverage & cost FAQ
How much paint do I need for a room?
A typical 4m × 3m room with 2.4m ceilings needs about 4 litres for two coats, once you've taken off a door and a window. Enter your own measurements above for an exact figure.
How much does 1 litre of paint cover in Australia?
About 16 square metres per coat for interior wall paint on a prepared surface. Primer covers less — around 12 to 14. Porous surfaces like render or bare brick can drop to 10.
Do I need to subtract doors and windows?
Yes, on anything bigger than a small room. A door and two windows is around 4.5 m², which on a small job is most of a litre. The calculator above takes them off for you.
How many coats of paint do I need?
Two is standard on a prepared surface in a similar colour. Go to three if you're covering a strong colour, painting over a patch repair, or working on bare plasterboard without primer.
Is it cheaper to buy 10L or 4L tins?
Almost always 10L per litre of paint — but not if you only need five litres and eight would go off in the shed. Put your prices in above and it'll work out the cheapest combination for the amount you actually need.
How much paint for the ceiling?
Work the ceiling out separately: length × width, no openings to subtract. Ceiling paint covers about the same as wall paint, and one coat is often enough over an existing painted ceiling in the same colour.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Coverage figures are typical published Australian rates and vary by product, surface and application method — always check the technical data sheet for the paint you're using. This calculator is a materials estimate to help you order and quote, not a specification.