One of the most common questions we get asked — and one of the most important ones to get right. An undersized air conditioner will never cool or heat your room properly. An oversized one will cost more to run and wear out faster. Here’s how to work it out.
The Simple Rule of Thumb
As a starting point, allow approximately 125-150 watts of cooling capacity per square metre of floor area. So a 20sqm bedroom needs roughly 2.5kW, a 30sqm living room needs around 3.5-4.5kW.
Why the Rule of Thumb Isn’t Always Enough
The square metre calculation is a starting point only. The actual system size depends on:
- Ceiling height — standard is 2.4m. Higher ceilings need more capacity.
- Sun exposure — a west-facing room with large windows needs 20-30% more capacity than a south-facing shaded room
- Insulation — older homes with poor insulation need larger systems
- How many people use the room — each person adds roughly 100W of heat load
- Appliances — a TV, computers, and lighting all add heat
Quick Reference Guide
| Room Size | Recommended Capacity |
| Up to 20sqm (small bedroom) | 2.5kW |
| 20-30sqm (bedroom/study) | 3.5kW |
| 30-45sqm (living room) | 5.0kW |
| 45-60sqm (open plan) | 7.0kW |
| 60-80sqm (large open plan) | 8.0-9.0kW |
If you’re unsure, call Jim on 0416 931 871. We’ll measure the space and recommend the right system — no obligation.