Floor Space Ratio, or Plot Ratio

When you are buying a new house block it’s important you understand how much of the block you can build on!

One way in which NSW councils prevent Over development is by prescribing a ‘Floor Space Ration’ (FSR). The same principle applies in WA but is called ‘Plot Ratio’.

The FSR of buildings on a site is the ratio of  ‘Gross Floor Area’ to Total Site Area.

Gross Floor Area is defined as – The sum of the internal floor area of each floor of a building  measured at a height of 1.4 m above the floor.

It includes  habitable rooms in a basement or an attic.

It excludes:

  • Stairs
  • Voids above a floor in 2 storey properties.
  • Non habitable storage including basement areas
  • Vehicular access and car parking
  • Terraces / Balconies with outer walls less than 1.4 metres high, and

To calculate, you multiply the site area by the FSR ratio.

For example

For a 800sqm site and a FSR of 0.5:1

Maximum Floor Space = 800 x 0.5 =  400sqm.

See Restrictions for  more posts  about what you can do on your land




  1. Belinda Mcclure

    Thus, an FSI of 2.0 would indicate that the total floor area of a building is two times the gross area of the plot on which it is constructed, as would be found in a multiple-story building.

    1. Brian Ashworth (Post author)

      That’s correct, Probably something like a townhouse on a small block.

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