Air conditioner room size chart
Find the room, read across to your climate. The bold figure is the unit size to look at, the one in brackets is the load the calculator works out for a 2.4m ceiling with average insulation and sun.
| Room | Cool | Temperate | Subtropical | Tropical |
|---|---|---|---|---|
| 10 m² small bedroom | 2.0 kW (1.2) | 2.0 kW (1.4) | 2.0 kW (1.6) | 2.0 kW (1.8) |
| 15 m² bedroom | 2.0 kW (1.8) | 2.5 kW (2.1) | 2.5 kW (2.3) | 3.5 kW (2.6) |
| 20 m² bedroom or study | 2.5 kW (2.4) | 3.5 kW (2.8) | 3.5 kW (3.1) | 3.5 kW (3.5) |
| 25 m² main bedroom | 3.5 kW (3.0) | 3.5 kW (3.5) | 5.0 kW (3.9) | 5.0 kW (4.4) |
| 30 m² lounge | 5.0 kW (3.6) | 5.0 kW (4.2) | 5.0 kW (4.7) | 6.0 kW (5.3) |
| 40 m² open living | 5.0 kW (4.8) | 6.0 kW (5.6) | 7.1 kW (6.2) | 7.1 kW (7.0) |
| 50 m² open plan | 6.0 kW (6.0) | 7.1 kW (7.0) | 8.0 kW (7.8) | 9.5 kW (8.8) |
| 60 m² big open plan | 8.0 kW (7.2) | 9.5 kW (8.4) | 9.5 kW (9.3) | 12.5 kW (10.5) |
The chart picks the next standard size up from the load, 2.0, 2.5, 3.5, 5.0, 6.0, 7.1, 8.0, 9.5, then 12.5 and 14 kW. A high ceiling, a west wall or a wall of glass moves a room up a row or two, so put the real room in the calculator above. Past 9.5 kW you’re looking at ducted or two units, and that’s heat load work.
A worked example
A 5m × 4m lounge in Brisbane, 2.7m ceilings, west facing with two big sliding doors.
- Area, 5 × 4 = 20 m²
- Subtropical band, 20 × 155 = 3,100 W
- Ceiling 2.7m instead of 2.4m, 2.7 ÷ 2.4 = ×1.125, so 3,488 W
- High sun, ×1.15, so 4,011 W
- Two large glass doors, ×1.10, so 4,412 W, or 4.41 kW
- Nearest standard unit up, 5.0 kW
The same room in Melbourne, 2.4m ceilings, south facing and shaded, works out at 20 × 140 × 0.93 = 2,604 W, a 3.5 kW unit. Same floor plan, one size apart. That’s why the plain square metres to kilowatts charts get it wrong so often.
The watts per square metre bands
| Climate | Where | Rate |
|---|---|---|
| Cool | Tasmania, Victorian highlands | 120 W/m² |
| Temperate | Melbourne, Sydney, Adelaide, Perth | 140 W/m² |
| Subtropical | Brisbane, northern NSW | 155 W/m² |
| Tropical | Darwin, Cairns, Townsville | 175 W/m² |
Multiply the room’s floor area by the rate and you have watts. Divide by a thousand for kilowatts, which is how Australian units are sold.
This is not an AS/NZS 5141 heat load calculation
Australia does have a standard here, AS/NZS 5141:2018, Residential heating and cooling systems, covering how these systems should be designed, selected and installed, and the way it sizes a system is a proper heat load assessment of your actual rooms. What no standard sets is the watts per square metre shortcut this page uses. Those bands are a rule of thumb published by installers and retailers, every Australian sizing tool we checked runs on the same rough method, and most present it as though it came from somewhere official. This one tells you which kind of number you’re getting.
Treat the answer as a starting point for a conversation with an installer, and expect a good one quoting a whole house to do the heat load properly rather than take a number off a web page. Nobody should order a ducted system off it.
Bigger isn’t safer, oversizing is a real problem
Rounding up hard backfires, and here’s how to explain that to a customer who wants the biggest unit on the wall.
- Short cycling. An oversized unit hits the set temperature fast, shuts down, and restarts a few minutes later. Compressors wear out on start ups, not on running hours.
- It never dries the air. Dehumidifying happens while the unit runs. A unit that only runs in short bursts leaves a room cold and clammy, exactly the complaint you get in Brisbane and Darwin, and exactly where people oversize the most.
- More money, twice. Dearer to buy, and inefficient at the part load it spends its whole life in.
Undersizing has its own problems. The unit runs flat out, never quite gets there, and costs a fortune on the hottest week of the year. The answer isn’t go big, it’s get the number roughly right, then check it properly.
What a proper heat load calculation does
A heat load calculation sees the building, not just floor area and a climate label. It counts
- Orientation, which way each wall and window faces, and when the sun hits it
- Glazing, the area, single or double, tinted, shaded or bare
- Insulation, ceiling, wall and floor R values, each on its own
- Infiltration, how much outside air leaks in, which is enormous in an old weatherboard and small in a new build
- Internal gains, people, cooking, a TV, lighting
For a single split in a bedroom, the rule of thumb is usually close enough to shop with. For a ducted system, do the heat load. Ducted is a lot of money, it’s sized zone by zone, and a guess and round job gives rooms that never balance and an owner who’s unhappy for a decade.
Want a room by room load without paying anyone? The federal government’s energy.gov.au points people to the FairAir website, run by AIRAH, the refrigeration and air conditioning engineers’ institute. Its cooling and heating load calculators ask about the windows, walls and shading this page can’t see.
Sources, energy.gov.au, Heating and cooling, and AIRAH, FairAir, both read 26 October 2026.
kW to BTU, for anyone reading a US spec sheet
Australian units are rated in kilowatts. American ones are in BTU per hour. 1 kW ≈ 3,412 BTU/h.
| BTU/h (US) | kW (Australia) | Nearest AU unit |
|---|---|---|
| 9,000 | 2.64 kW | 2.5 or 3.5 kW |
| 12,000 | 3.52 kW | 3.5 kW |
| 18,000 | 5.28 kW | 5.0 kW |
| 24,000 | 7.03 kW | 7.1 kW |
Worth knowing when a customer forwards you a link to something they found online.
Installing it is licensed work
Fitting a split is licensed four ways, and the one people miss is the state licence.
- Refrigerant, everywhere. The Australian Refrigeration Council says “A Refrigerant Handling Licence is required for any activity involving a risk of a refrigerant emission.” Its list includes installing and commissioning the equipment “(whether or not refrigerant is present)”. The business buying and holding the gas needs a refrigerant trading authorisation too. It’s federal, the same in every state.
- Your state’s licence, on top. NSW wants an air conditioning and refrigeration licence or certificate, Queensland puts it under the QBCC’s mechanical services licences, and Victoria wants a plumbing registration with the Building and Plumbing Commission to install, replace or repair a reverse cycle unit. We haven’t read SA, WA, Tasmania, the ACT or the NT on this one, so check yours before you quote.
- The wiring. Connecting it to fixed wiring is licensed work, and the ARC licence alone doesn’t cover it. In NSW the air conditioning licence does, “This includes any associated electrical wiring that would otherwise be done by an electrician.” Everywhere else, use a licensed electrician unless your regulator says your ticket covers it. A hard wired split or a ducted unit usually wants its own circuit, so on an older switchboard the job can be bigger than the customer expects.
- Condensate and mounting. Drains have to fall somewhere legal, and outdoor units near a boundary can run into noise rules that vary by state and council.
Doing the electrical side of someone else’s install? Look at the switchboard before you quote and price that work separately. It’s where these jobs blow out.
Sources, ARC, What work requires a refrigerant handling licence?, and DCCEEW, Refrigeration and air conditioning (last updated 30 April 2026), both read 26 October 2026. NSW Government, Air conditioning and refrigeration work (last updated 23 October 2026), read 26 October 2026. QBCC, Available licences, and the Victorian air conditioning fact sheet, checked for the Yamate compliance list 13 October 2026.
Sizing one for your own place? The number above is enough to shop with, but the rooms have to be seen before it’s real. Find an air conditioning installer near you, ask them to check the sizing on site, and check their ARC licence on Look for the Tick before they start.
Sized it up. Now get the quote out before someone else does.
Yamate turns your site notes into a quote the customer can accept on their phone, then an invoice, then a payment, with GST worked out and payment reminders sent once you switch them on.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberAir conditioner sizing FAQ
What size air conditioner do I need for a room in Australia?
Multiply the floor area by 120 to 175 watts per square metre depending on your climate, 140 W/m² suits Melbourne, Sydney, Adelaide and Perth. A 20 m² room in a temperate climate comes out around 2.8 kW, so you would look at a 3.5 kW unit. The room size chart on this page has 10 to 60 m² done for every climate.
Is there an Australian Standard for air conditioner sizing?
AS/NZS 5141:2018 covers residential heating and cooling systems, their design, selection and installation, and the way it sizes a system is a proper heat load assessment. No standard sets the watts per square metre shortcut used by online tools, including this one. Treat any web answer as a starting point rather than a specification.
Is it better to oversize an air conditioner?
No. An oversized unit short cycles, wears the compressor on repeated start ups, and never runs long enough to pull moisture out, so the room ends up cold and clammy. It also costs more to buy and runs inefficiently at part load.
How many BTU is a 3.5 kW air conditioner?
About 11,900 BTU per hour, since 1 kW is roughly 3,412 BTU/h. Going the other way, a 12,000 BTU American unit is about 3.5 kW.
Does ceiling height change the air conditioner size?
Yes, you are cooling volume, not floor area. A 2.7m ceiling is 12.5% more air than a standard 2.4m one, and a 3m ceiling is 25% more. The calculator above scales for it.
When do I need a proper heat load calculation?
For any ducted system, and for anything unusual, big glazing, a poorly insulated old house, a west facing room that bakes. A heat load counts orientation, glazing, insulation and air leakage, which a square metre rule of thumb cannot see.
Who can install a split system in Australia?
Anyone installing one needs an ARC refrigerant handling licence, and the business needs a refrigerant trading authorisation to buy the gas. That is federal. NSW, Queensland and Victoria also want a state licence or registration, and connecting it to fixed wiring is licensed electrical work, which in NSW the air conditioning licence covers.
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. This is a rule of thumb guide, not a specification and not an AS/NZS 5141 heat load calculation. The watts per square metre bands used here are the shortcut Australian installers publish, not figures set by a standard. A proper heat load calculation counts orientation, glazing, insulation and air infiltration, and is what you should be doing for a ducted system or an unusual room. Installation involves licensed refrigerant handling, a state licence in some states and licensed electrical work.