Sydney is about 1.8 times smaller than Ho Chi Minh City.

Ho Chi Minh City is approximately 6,773 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 56.25% the size of Ho Chi Minh City.
Tip: This to-scale comparison of Ho Chi Minh City vs. Sydney uses the Mercator projection, which distorts the size of regions near the poles.
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