Granny flat floor area calculator
Measure each room inside the walls. Set a room to 0 if you don't need it. Nothing is sent anywhere.
The 70 m² rule
Under the state's residential rules (the R-Codes), a granny flat (an "ancillary dwelling") is limited to an internal floor area of 70 m². The state's guidance says that's enough for a one or two-bedroom home. There's no minimum lot size any more, and it can be attached to the house, inside it, or separate.
How to measure
The R-Codes guidance says internal floor areas are measured from the finished inside surface of the walls. That's why the calculator asks for room sizes inside the walls. The outside footprint of the building will be bigger.
We haven't found clear state guidance on whether every council counts things like verandahs or a store room the same way, so check with your council before you finalise the plans.
Bigger than 70 m²?
Some councils allow more on large or rural lots through their own local planning policies, so check yours. Otherwise, anything over 70 m² needs planning approval and may not be supported. A granny flat always needs a building permit too.