What Size Air Conditioner Do I Need? A Sydney Room-by-Room Guide
Buying an air conditioner that's too small means it'll struggle to cool the room and run non-stop. Too large and it'll cool the room too quickly without properly dehumidifying — leaving the air feeling cold but clammy. Getting the size right is essential.
At Oceania Appliances in Wetherill Park, we help Sydney homeowners and apartment dwellers pick the right air conditioner capacity every day. Here's how to do it properly.
How Air Conditioner Capacity Is Measured
Air conditioner cooling capacity is measured in kilowatts (kW). This tells you how much heat the unit can remove from the room per hour. Common sizes for residential split systems in Australia are 2.5kW, 3.5kW, 5.0kW, 7.1kW, and 9.0kW.
Basic Sizing Rule of Thumb
As a starting point, allow approximately 125W per square metre for a standard room (ceiling height under 2.7m, shaded window, moderate climate).
| Room Size | Starting Capacity | Adjust for Hot/Sunny Room |
|---|---|---|
| Up to 20 m² | 2.5 kW | 3.5 kW |
| 20–30 m² | 3.5 kW | 5.0 kW |
| 30–45 m² | 5.0 kW | 6.0–7.1 kW |
| 45–60 m² | 7.1 kW | 8.0–9.0 kW |
| 60–80 m² (open plan) | 9.0 kW | 10–12 kW |
Factors That Increase the Capacity You Need
- North or west-facing rooms receive more sun and heat up significantly more than south-facing rooms
- Large or unshaded windows bring in more solar heat
- Poor insulation (older homes, uninsulated ceiling) allows heat to penetrate
- High ceilings (above 2.7m) increase the volume of air to cool
- Open-plan spaces require more capacity than the floor area alone suggests
- Sydney's humidity in summer means the unit has to work harder to dehumidify
Room-by-Room Guide for Sydney Homes
Main Bedroom (12–20 m²)
A 2.5–3.5kW unit is usually right. If the bedroom faces west (afternoon sun), lean toward 3.5kW. Sydney summer nights are warm and humid — a correctly sized unit that runs at a lower speed all night is more comfortable than an oversized one that cycles on and off.
Second Bedroom (10–15 m²)
2.5kW is usually sufficient. The smallest residential split systems are 2.5kW.
Living/Dining Area (25–45 m²)
The most common area requiring a larger unit. For a standard open-plan living/dining in a Sydney house, 5.0–7.1kW is typical. For a larger open-plan area that connects to a kitchen, go 7.1–9.0kW.
Sydney Apartment Living Area (25–35 m²)
Sydney apartments on higher floors can be very warm in summer due to solar heat gain through glass. Even a 25m² apartment living area may need a 5.0–6.0kW unit if it has north or west-facing windows.
Don’t Forget Heating
Sydney winters are mild but cold at night. All modern split systems are reverse-cycle, meaning they provide both cooling and heating. A correctly sized split system in a Sydney bedroom typically costs $0.80–$1.50 per night to run on heating overnight — far cheaper than a plug-in heater.
Get It Right from the Start
At Oceania Appliances, we stock Daikin, Panasonic, Samsung, and LG split systems across the full capacity range. Come in with your room dimensions and we'll help you pick the right model for your budget and room. Free delivery across Sydney.
Visit us at 2/14 Centre Place, Wetherill Park — open 7 days, 10 am to 8 pm.