Free tool for Melbourne homeowners
Air Conditioner Size Calculator
Work out what size split system your room needs. Enter the room size, ceiling height, sun exposure and insulation to get a recommended kW range, calibrated for Melbourne homes. Takes about 20 seconds.
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Recommended size
Your room needs about
Based on a typical Melbourne living room
5.0 kW unit class
Calculated load: 4.6 kW (range 4.1 to 5.1 kW)
This is an indicative guide for a single room. Final sizing must be confirmed by a licensed installer, who will also check the electrical circuit, outdoor unit position and heating capacity. Every assumption used is published below.
How the sizing works
The calculator uses the same method installers use for a first estimate: a base capacity per square metre for Melbourne's climate, adjusted for the things that change how hard a unit works.
Base rate by room
Bedrooms need about 115 watts per square metre, living areas 140, and open plan spaces with a kitchen 150.
Ceiling height
Capacity scales with air volume. A 2.7 m ceiling adds about 13 percent to the load, a 3 m ceiling about 25 percent.
Sun and glass
Full afternoon sun adds 15 percent. Large glass areas add up to 20 percent more, because windows let heat in far faster than walls.
Insulation
Good ceiling and wall insulation trims the load by 10 percent. Poor insulation in older homes adds 15 percent.
The result is matched to the closest common split system size: 2.5, 3.5, 5.0, 6.0, 7.1, 8.0 or 9.2 kW. Slight oversizing is fine, but a heavily oversized unit short cycles, dehumidifies poorly and costs more to buy, which is why the tool never jumps more than one size up.
Method reviewed: July 2026. Base rates reflect common Australian industry sizing guidance for Melbourne's climate zone. Sizing a heat pump for a Melbourne winter instead? That tool sizes the same units on the heating load, which usually governs here.
Method, sources and review
We publish the working behind this tool rather than asking you to trust the number. The assumptions above are the ones the calculator actually uses. These are the sources they come from.
- Capacity, efficiency and performance figuresManufacturer specifications (Mitsubishi Electric, Daikin, Fujitsu, Panasonic, ActronAir, Brivis, Braemar)
- Sizing recommendationsMelbourne heating and cooling loads (Climate zone 6, heating dominant)
Which size suits which room
| Unit size | Room size guide | Typical rooms |
|---|---|---|
| 2.5 kW | Up to 20 sqm | Bedrooms, studies, small offices |
| 3.5 kW | 20 to 30 sqm | Large bedrooms, small living rooms |
| 5.0 kW | 30 to 40 sqm | Living rooms, master suites |
| 6.0 to 7.1 kW | 40 to 55 sqm | Open plan living and dining |
| 8.0 to 9.2 kW | 55 to 70 sqm | Large open plan areas |
| Over 9.2 kW | 70 sqm plus or multiple rooms | Consider a multi head or ducted system |
Sizing one room is only half the story. If you are conditioning several rooms, a multi head split system runs them all from one outdoor unit, and beyond about 70 square metres a ducted reverse cycle system is usually better value per room. For single rooms, see our split system air conditioning and split system heating pages, or compare brands on our air conditioning brands page.
Sizing for Melbourne homes
Melbourne sizing has a twist most national guides miss: winter matters more than summer. A reverse cycle split system spends far more hours heating than cooling here, and heating capacity falls on cold nights right when you need it most. That is why the tool flags the heating capacity check on every result.
Housing stock matters too. Older weatherboards in suburbs like Brunswick leak heat and usually need the insulation set to poor, while a modern apartment in Southbank with one glass wall needs the full sun and large windows settings even though it is small. When in doubt, run the calculator twice with both settings and treat the gap as your shortlist range.
Wondering what the unit will cost to run once it is in? Try our running cost calculator next.
Air conditioner sizing FAQs
What size split system do I need for a bedroom?
Most Melbourne bedrooms are 10 to 16 square metres, which lands comfortably in the 2.5 kW class. Go to 3.5 kW for a large bedroom over 20 square metres, a room with a west facing window, or a poorly insulated older home.
What size air conditioner do I need for a 4 by 4 room?
A 4 by 4 metre room is 16 square metres. As a bedroom that is about 1.8 to 2.2 kW of load, so a 2.5 kW unit fits. As a living room with average sun and insulation it is about 2.2 to 2.6 kW, which still suits a 2.5 kW unit, or 3.5 kW with full sun or high ceilings.
Is it better to oversize or undersize an air conditioner?
Neither extreme. An undersized unit runs flat out and never quite gets there on hot days. A heavily oversized unit short cycles, which wears the compressor, dehumidifies poorly and wastes money upfront. One size class above the calculated load is the practical ceiling.
Does ceiling height change what size I need?
Yes. Sizing follows air volume, not just floor area. A 3 metre ceiling holds a quarter more air than a standard 2.4 metre ceiling, so the same floor plan needs about 25 percent more capacity.
Why does heating capacity matter more than cooling in Melbourne?
Melbourne has far more heating days than cooling days, and a heat pump's output drops as the outdoor temperature falls. A unit sized only for summer can fall short on a 3 degree morning. Check the rated heating capacity matches your calculated size, and when the two differ, size for heating.
Sizing is a starting point. The install makes it work.
Our licensed technicians confirm the right size on site, position the unit for airflow, and back the installation with a 7-year guarantee. Quotes are free across Melbourne.
Book a free sizing assessment Prefer to browse first? See split systems Or call 0412 769 022.