As a rough guide for the Cairns and FNQ climate, a small bedroom up to 15m² suits a 2.5kW air conditioner, a medium 15–40m² room needs around 3.5–5kW, and an open-plan 40–60m² living area may need 6–8kW or more. Getting the size right matters as much for humidity as for temperature, so it's worth a proper check.
Quick sizing guide by room
| Room size | Typical use | Approx. capacity |
|---|---|---|
| Up to 15m² | Bedroom, study | 2.5kW |
| 15–40m² | Large bedroom, small living | 3.5–5kW |
| 40–60m² | Open-plan living/kitchen | 6–8kW |
| 60m²+ | Whole zones / large open plan | 8kW+ or ducted |
These are starting points, not final answers. The right capacity for your room can shift up or down once the details are factored in.
What affects the size you need
- Ceiling height — high or raked ceilings mean more air to cool
- Window orientation — west and north-facing glass adds a lot of heat load
- Insulation — older, poorly insulated FNQ homes need more grunt
- Sun and shade — an exposed room runs hotter than a shaded one
- Open plan — rooms that flow together are sized as one space
Why bigger isn't better
It's tempting to oversize "to be safe", but an oversized unit cools the air fast and then short-cycles — switching off before it has pulled the humidity out. In Cairns that leaves a room cold but clammy, and wastes power. An undersized unit runs flat out and never quite gets there. Correct sizing is the sweet spot for comfort, efficiency and humidity control.
The FNQ factor
Our heat and humidity are unforgiving, so sizing here isn't the same as down south. We always recommend a quick site inspection to measure the room, check orientation and insulation, and match the capacity properly — it's free, and it's the difference between a system that just copes and one that's genuinely comfortable.
The short version
Roughly 2.5kW for a bedroom, 3.5–5kW for a medium room, 6–8kW for open-plan living — then adjust for ceilings, windows and insulation. When in doubt, get it measured.
Related: How much does air conditioning cost in Cairns? · Ducted vs split system · All FAQs