San Francisco is about 1.7 times smaller than Stockholm.

Stockholm (map shows its 47 named neighbourhoods; the area covers the whole city) is approximately 207 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 58.33% the size of Stockholm.
Tip: This to-scale comparison of Stockholm vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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