Sydney is about 4.3 times bigger than Dallas.

Dallas is approximately 880 sq km, while Sydney (the 30 councils of metropolitan Sydney, without the Blue Mountains, Hawkesbury, Wollondilly and the Central Coast) is approximately 3,810 sq km, making Sydney 333% larger than Dallas.
Tip: This to-scale comparison of Dallas vs. Sydney uses the Mercator projection, which distorts the size of regions near the poles.
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