Sydney is about 31 times bigger than San Francisco.

San Francisco (including the city proper only) is approximately 121 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 3,049% larger than San Francisco.
Tip: This to-scale comparison of San Francisco vs. Sydney uses the Mercator projection, which distorts the size of regions near the poles.
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