AUSTRALIANS are piling on sitting rooms, family rooms, studies and extra bedrooms at the fastest rate in the world, with the size of our homes overtaking those in the US as the world's biggest.

The typical size of a new Australian home hit 215 square metres in the past financial year, up 10 per cent in a decade, according to Bureau of Statistics data compiled for Commonwealth Securities.

The average size of new homes around the world in square metres.

US figures show the size of new American homes shrinking from 212 square metres before the financial crisis to 202 square metres in September.

New homes in other parts of the world are far smaller, with Denmark the biggest in Europe at 137 square metres and Britain the smallest at 76 square metres.