The subdivision potential of your land and how/if you can subdivide will be determined by the following:

• The zoning(allowable use) and density coding of your property on your Local Government or Councils “Local Scheme Map”, and subsequently your ability to meet relevant requirements in the State governments Residential Design Codes and the Local Government Scheme Text. The map will show the density code of all residential zoned land in the schemes boundaries.
• The performance requirements specified in West Australian Planning Commissions (WAPC) Residential Design Codes, which stipulate minimum and average lot sizes for residential density coding annotated on a relevant  Scheme map. You can learn how this will impact your ability to subdivide and how important it is on the rules for subdividing land in Western Australia page of our website.
• If you wish to retain the existing dwelling as part of a subdivision, the orientation, positioning and condition of the dwelling may impact the subdivision potential of the project.

There is a whole section with detailed explanation on subdivision and development potential available for your benefit in the 225 page Infill Property Developer Guidebook.