What Size Air Conditioner Do I Need? How to Calculate the Right Size AC for Your Home

Comfort, Efficiency, and Energy Savings All Start with the Right Fit.

Choosing the right size air conditioner is one of the most important steps in creating a comfortable, energy-efficient home. Go too small, and your system will struggle to keep up. Too big, and it can become noisy, inefficient, and expensive to run.

So how do you figure out what size air conditioner you need? Let’s break it down.

Step 1: Measure the Area of Your Space

Start by measuring the floor area (in square metres) of the room or open space you want to cool or heat.

Formula:

Room size (m²) = Length × Width

For example: A space that is 5m × 4m = 20m²

Useful tip: If you're unsure of your room dimensions, try searching online for your home's floor plan (especially if it was recently built or sold). Real estate listings often include detailed floor plans with room measurements.

Step 2: Adjust for Ceiling Height

The amount of air that needs conditioning depends on the height of your ceiling. Use the formula below to calculate your system’s cooling capacity in watts:

• 2.4m ceilings: Multiply your living area by 150

• 2.7m ceilings: Multiply your living area by 160

• 3m ceilings: Multiply your living area by 175
  

Example:

A 20m² room with a 2.7m ceiling: 20 × 160 = 3,200 watts = 3.2kW air conditioner

Step 3: Consider Other Influences

While floor size and ceiling height give you a solid estimate, several other factors can impact the final recommendation:

• Insulation quality – Better insulation reduces energy needs

• Sunlight exposure – Large east or west-facing windows increase heat gain

• Room usage – Kitchens and offices may need more cooling

• Occupancy – More people = more heat

• Climate zone – Hotter regions may require higher capacity

If in doubt, it may be best to size up.

Why Getting the Size Right Matters

• Comfort: Maintains a consistent temperature 

• Efficiency: Saves you money on power bills 

• Durability: Avoids overworking your system 

• Humidity Control: Keeps the air fresh and balanced

Still Not Sure? We Can Help

At On Call Air-Conditioning & Refrigeration, we take the guesswork out of air con sizing. Our team provides on-site assessments, considering your room layout, insulation, usage, and ceiling height to recommend the ideal system.

We’re based in Berkshire Park and service the Hawkesbury, Penrith, Blacktown and most other parts of Greater Western Sydney, and surrounding suburbs. Plus, as an approved provider under the NSW Energy Savings Scheme (ESS), we can help you access rebates of up to $1,400 for eligible energy-efficient systems.

Comfort Starts With A Call

If you’re ready for an upgrade or a brand new system, On Call Air-Conditioning & Refrigeration makes it easy and stress-free, with expert advice and friendly service. You deserve a comfortable, efficient home that meets the demands of Sydney’s unique climate.

Contact us today for free advice and experience top-notch service.