Canberra is about 4.7 times smaller than Sydney.

Sydney (the 30 councils of metropolitan Sydney, without the Blue Mountains, Hawkesbury, Wollondilly and the Central Coast) is approximately 3,810 sq km, while Canberra is approximately 814 sq km, making Canberra 21.37% the size of Sydney.
Tip: This to-scale comparison of Sydney vs. Canberra uses the Mercator projection, which distorts the size of regions near the poles.
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