San Francisco is about 1.7 times smaller than Antwerp.

Antwerp (map shows its 62 named neighbourhoods; the area covers the whole city) is approximately 208 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 58.11% the size of Antwerp.
Tip: This to-scale comparison of Antwerp vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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