What Size Split System Do I Need? An Australian Room-by-Room Guide [2026]

A rough formula gets you most of the way there: multiply your room's floor area in square metres by 0.15, and the result is your starting capacity in kilowatts. A 20m² bedroom lands at 3kW, which rounds to a 3.5kW unit.

A 50m² open-plan living area lands at 7.5kW, suggesting a 7.1kW or 8kW system. The formula is a starting point, not a final answer. Ceiling height, insulation, window direction, and the climate you live in all shift the number.

This guide walks through each factor so you end up with a size that suits your room, not one that sounded right on a spec sheet. Once you have the number, we show you what's available at that capacity in our range.

In this article

• The basic sizing formula
• Room-by-room kW guide
• What else changes the size you need?
• Does your state affect the calculation?
• Shop our range by size
• Can one split system cover multiple rooms?
• Frequently asked questions

The basic sizing formula

The formula Australian HVAC professionals use as a baseline:

The 0.15 figure comes from standard Australian industry sizing guidance for moderate climate zones. If you are in Queensland or Western Australia, increase it to 0.17 to 0.18. If you are in coastal New South Wales or Victoria with good insulation, 0.13 to 0.14 can work for shaded rooms.

Rather than doing the maths yourself, use our split system size calculator. Input your room dimensions, ceiling height, and sun exposure and it returns a specific kW recommendation in about 30 seconds.

Room-by-room kW guide

The table below covers the most common room types in Australian homes. Use it as a starting point, then apply the adjustments in the next section.

Room type	Typical size	Recommended kW	Notes
Small bedroom / study	Up to 15m²	2 to 2.5 kW	Standard ceiling, good insulation
Master bedroom	15 to 25m²	2.5 to 3.5 kW	Add 0.5kW for west-facing window
Medium living / dining	25 to 40m²	3.5 to 5 kW	Use 5kW if ceiling height exceeds 2.7m
Large open-plan living	40 to 60m²	5 to 7.1 kW	Kitchen heat loads push toward 7kW+
Very large open-plan	60 to 80m²	7.1 to 8 kW	Consider multi-head or ducted above 80m²
Home office	10 to 20m²	2 to 2.5 kW	Add for computers/servers generating heat

These sizes align with the most common split system variants available in Australia: 2, 2.5, 3.5, 5, 6, 7.1, and 8kW. There is no need to find an exact match. Choosing the next size up is fine. Choosing two sizes up is where the short-cycling problems start.

What else changes the size you need?

Four variables adjust the formula significantly.

1. Ceiling height

The 0.15 formula assumes a standard 2.4m ceiling. Every 0.3m of extra ceiling height increases the air volume to cool by roughly 12%.

A room with 3m ceilings needs about 20% more capacity than the formula suggests. Older Queensland homes with high ceilings often need a full size up from the floor-area estimate.

2. Insulation

A well-insulated room with ceiling batts, wall insulation, and double-glazed windows can get away with 15 to 20% less capacity.

An older weatherboard home with no ceiling insulation and single glazing needs 20 to 30% more. If you are not sure of your insulation level, assume average and size to the middle of any recommended range.

3. Window direction and size

North and west-facing windows are the biggest heat sources in Australian homes.

A room with large north or west-facing glass during a summer afternoon can have twice the heat load of the same room facing south.

Add at least 10% capacity for west-facing windows, more for large or poorly shaded glazing.

4. Number of occupants

Each person in a room generates roughly 0.1kW of heat continuously.

For most rooms this barely registers. For a home gym or a meeting room with six or eight people, it matters. Add 0.1kW per person above two when sizing for regularly occupied spaces.

Does your state affect the calculation?

Yes. Australia spans six climate zones, and the required cooling and heating capacity varies by region.

Region	Adjust formula by	Priority
Queensland, NT, northern WA	+15 to 20% cooling capacity	Cooling dominant
NSW, ACT (coastal and inland)	Use base formula	Balanced heating/cooling
Victoria, Tasmania, ACT alpine	Match heating kW to cooling kW	Heating dominant
Perth, Adelaide (south-facing rooms)	Use base formula; check low-temp heating	Both seasons important

In Victoria and the ACT in particular, the heating capacity at low ambient temperatures (below 2°C) matters as much as the cooling rating.

Daikin, Fujitsu, and Mitsubishi Electric all publish low ambient heating performance specs. Not all brands do. Check the spec sheet before buying if you live somewhere that drops below freezing.

Shop our range by size

All three models below are available across the full residential size range, from 2kW bedroom units to 8kW open-plan systems. Each ships with the full Australian manufacturer warranty.

Can one split system cover multiple rooms?

A single split system is designed for one space. If you want to cool two or three rooms from one outdoor unit, you need a multi-head split system.

These connect multiple indoor heads to one outdoor condenser and can be more cost-effective than running separate outdoor units for each room.

For whole-home comfort across five or more rooms, ducted air conditioning is generally a better fit.

Ducted systems use ceiling outlets in each room and one central unit, giving you consistent temperature across the whole floor plan without multiple wall units.

The typical rule: one room needs one split system. Two or three rooms from the same area can share a multi-head. Four rooms or more is usually ducted territory, depending on the layout of the home.

Not sure which system suits your home? Our team is available 7 days a week on 1300 156 466 or via our contact page.

Frequently asked questions

What size split system do I need for a 20m² bedroom?

A 2.5kW unit. The formula (20 × 0.15 = 3kW) suggests a 3kW system, but 2.5kW covers most Australian bedrooms at this size with standard ceiling height and reasonable insulation.

Go to 3.5kW if the room has west-facing windows, poor insulation, or a ceiling above 2.7m.

What size split system do I need for an open-plan kitchen and living area?

For a combined area of 40 to 60m², a 6kW to 7.1kW unit. Kitchens add heat load beyond what the floor area suggests, so err toward the top of any range.

A 5kW unit will work in a 40m² space with good insulation and shade; a 70m² open-plan with a gas cooktop and west-facing glass needs the full 7.1kW or an 8kW system.

Should I always go one size up to be safe?

One size up is usually fine and occasionally a good idea for future-proofing. Two sizes up causes short-cycling: the unit reaches the set temperature too quickly, shuts off, restarts repeatedly, and never runs long enough to dehumidify the room properly.

In humid climates like Queensland and coastal New South Wales, short-cycling leaves the room feeling clammy even at the right temperature.

What is the most common sizing mistake Australians make?

Undersizing the living area and oversizing the bedroom.

The living room gets the small leftover unit from a previous home; the bedroom gets a 3.5kW unit when a 2.5kW would do.

Getting it right in both rooms reduces running costs and extends the life of each unit.

What size split system do I need for a whole house?

A single split system cannot cool a whole house. You need either a multi-head system (two or three indoor heads from one outdoor unit) or ducted air conditioning.

As a rough guide, a four-bedroom house in Sydney or Melbourne requires around 12kW to 16kW of total cooling capacity. Browse our ducted systems range for whole-home options.