Use the Canberra Extension Calculator to get better estimates

How much will something like this cost to build?

Use this app to help sense‑check your requirements and budget. It also generates a PDF with a detailed budget breakdown.

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The app and a floor‑rate calculation can only give a ballpark cost. I can help with refining your requirements and getting a better understanding of potential costs. To discuss your project in detail contact me. It’s free!

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Budget estimation FAQ’s

What is the average cost per square meter for a home extension in Canberra?

The Canberra Extension Calculator uses the following per‑square‑metre rates:

  • Base rate $5,000/m2

  • Bathrooms and wet areas $6,000/m2

  • Kitchens $6,000/m2

  • Garages $1,800/m2
These are based on 2025 construction costs for a single story extension on a standard block. They are derived from recently completed projects.

What are the problems with per metre construction rates?

When asked for a ballpark construction cost, most Canberra builders typically quote a rate of $5,000 per square metre. This presents homeowners with two challenges. Firstly, you need a good grasp of room sizes. Secondly, this average rate needs to be adjusted for the varying costs of building different types of rooms. In addition, these rates don’t account for things like pre-construction costs, steep blocks, high-end inclusions, or renovations to the existing house. Finally, projects with a floor area of less than 35m2 should be costed at a higher rate as they lack economies of scale.

What are the average room sizes in Australia?

The Canberra Extension Calculator uses the following default room sizes:

  • Bedroom Small: 2.8m x 3.0m

  • Bedroom Large: 3.1m x 4.0m

  • Master Bedroom: 3.4m x 4.5m

  • Ensuite: 1.4m x 3.0m

  • Bathroom: 2.5m x 3.0m

  • Laundry: 1.8m x 2.5m

  • Lounge: 3.5m x 4.0m
These are indicative sizes to help with esitmmating floor areas. Room sizes can vary greatly based on design and personal preference.

What are the standard sizes for garages and carports in Australia?

The Canberra Extension Calculator use following sizes:

  • Carport Single: 3.0 x 6.0m

  • Carport Double: 6.0 x 6.0m

  • Garage Sinlge: 3.6 x 6.0m

  • Garage Double: 6.0 x 6.0m
These exceed the minimum requirements of the Australian Standard AS2890.1. This ‘bit extra’ allows some storage and make the carport or garage more practical.

How do I reduce the risk of my extension going over budget?

Take the time in the early stages of your project to develop comprehensive requirements. Audit your existing house. Make a detailed list of all the items to be renovated, repaired, updated or replaced. As your project progresses, the cost of making even minor changes in scope increases. Making changes once construction has started is always the most expensive way of doing things!