This is a really common question. The Australian Standards AS1428.1 requires a minimum clear opening of 850mm to provide clearances for the 90th Percentile wheelchair.  Practically, smaller door openings will provide for smaller wheelchairs, however, the Standards have been derived, with a line in the sand and, provided your doorway is a min 850 clear of any obstructions, it is lawful.

The reality is that some wheelchairs can fit through much smaller openings safely, and other wheelchairs are simply too wide, even for an 850 clear opening. In a private house, you could, by using personal ergonomic measurements, design the door widths and corridors to suit the resident's clearance requirements and not follow the standards at all.

There are other exceptions to the door width required by the Standards. In NSW Nursing homes, for instance, doorways are required to be wider than the minimum in the standards, especially when occupants are evacuated in emergency situations while remaining in their beds. Clearances are needed to fit the bed through the door (obviously without tipping it sideways, since there is a resident on the bed!) Details for those doorway clearances and corridor widths are stipulated in the building code and big problems (with big rectification costs) are caused by mere millimetre indiscretions.

There's more to traversing through a door opening than simply getting the door size right. There are circulation space requirements either side of the door to enable a person to operate it, and there are door handle requirements, as well as the force required to operate the door. All of these limitations mean that you'd better obtain the right advice first up, to avoid costly rebuilds. Contact Sydney Access Consultants for a review of  your project.