Braunschweig is about 1.6 times bigger than San Francisco.

San Francisco (including the city proper only) is approximately 121 sq km, while Braunschweig is approximately 193 sq km, making Braunschweig 59% larger than San Francisco.
Tip: This to-scale comparison of San Francisco vs. Braunschweig uses the Mercator projection, which distorts the size of regions near the poles.
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