How to Choose the Right Air Conditioner Size for Your Room
Buying the wrong size air conditioner is one of the most common mistakes homeowners make. Too small and it runs constantly, struggles on hot days and wears out faster. Too large and it short-cycles — switching on and off frequently without properly dehumidifying the air, leaving the room feeling cool but clammy. This guide walks you through how to size an air conditioner correctly for every room in your home.
Understanding Kilowatts (kW)
Air conditioner capacity is measured in kilowatts (kW). This refers to the cooling output — not the electricity input. A 2.5kW unit produces 2.5kW of cooling. The electricity it uses will be less — typically around 0.6–0.9kW for an efficient inverter unit. When comparing models, always check the kW cooling capacity, not the electricity consumption figure.
The Basic Room Size Guide
| Room Size | Recommended Capacity | Typical Use |
|---|---|---|
| Up to 20m² | 2.0–2.5kW | Small bedroom, study, studio |
| 20–30m² | 2.5–3.5kW | Standard bedroom, medium room |
| 30–45m² | 3.5–5.0kW | Large bedroom, small living room |
| 45–60m² | 5.0–7.0kW | Medium living/dining area |
| 60–80m² | 7.0–9.0kW | Large open-plan living area |
| 80m²+ | 9kW+ or multiple units | Very large open plan, combined spaces |
Factors That Affect Sizing
Room size is the starting point, but several other factors affect how much cooling capacity you actually need:
- Ceiling height — Rooms with ceilings above 2.7m have more air volume to cool. Increase capacity by 10–15% for high ceilings
- Sun exposure — A north or west-facing room that receives afternoon sun all year round needs more cooling capacity than a south-facing room. Add 10–20% for strong sun exposure
- Insulation — Older homes with minimal insulation lose cooling quickly. Consider adding 10–15% if your insulation is poor
- Number of people — Each person in a room generates heat. For rooms regularly occupied by 4+ people, add 300–500W per person
- Heat-generating appliances — A kitchen with an oven or large TV generates significant heat. Account for this if you're cooling a combined kitchen-living space
- Open plan flow — If your living area flows into a hallway or adjacent rooms, the effective space is larger than the room's footprint suggests
Practical Examples
Standard Sydney bedroom (12–15m², moderate sun): 2.5kW is typically sufficient. If the bedroom faces west and heats up significantly in the afternoon, consider 3.5kW.
Open-plan kitchen-living-dining (55–65m²): 7.0–8.0kW is typically appropriate. If the space has north-facing glass doors or high ceilings, consider 9kW.
Apartment living room (30–40m², insulated building): 4.0–5.0kW usually works well. Modern apartment buildings with double glazing retain cooling efficiently.
Don't Undersize to Save Money
A smaller unit is cheaper to buy but will cost more to run if it has to work constantly to maintain temperature. An undersized unit also wears out faster, as the compressor never gets adequate rest. Spending an extra $100–$200 upfront for the right capacity pays dividends over the unit's life.
Get Advice Before You Buy
At Oceania Appliances, we're happy to help you work out the right capacity for your space. Contact us and tell us your room size, ceiling height and sun exposure — we'll recommend the right unit from our current stock. We deliver split systems across Sydney with same-day or next-day options available.