From
Rank - Statistical Division/District - Preliminary Estimated Resident Population, 2005 [2]
1 Sydney, New South Wales 4,254,894
2 Melbourne, Victoria 3,634,233
3 Brisbane, Queensland 1,810,943
4 Perth, Western Australia 1,477,815
5 Adelaide, South Australia 1,129,269
5 cities totalling over 12 million out a national population of 20 million. Pretty urban, although each city does cover a reasonable area. This means more riding in traffic compared with more compact cities.
For comparison, from
Rank - Urban sub-area - Population - Ceremonial county - Notes
1 London 7,172,091 Greater London, City of London Greater London administrative area only
2 Birmingham 970,892 West Midlands Metropolitan district, minus Sutton Coldfield, which is counted separately, plus areas in the north of the Metropolitan Borough of Solihull (Castle Bromwich etc)
3 Liverpool 469,017 Merseyside Metropolitan district, plus some areas outside
4 Leeds 443,247 West Yorkshire
5 Sheffield 439,866 South Yorkshire Excludes the suburbs of Beighton, Chapeltown and Mosborough/Highlane