Des Moines is about 1.9 times bigger than San Francisco.

San Francisco (including the city proper only) is approximately 121 sq km, while Des Moines (map shows its 58 named neighbourhoods; the area covers the whole city) is approximately 228 sq km, making Des Moines 89% larger than San Francisco.
Tip: This to-scale comparison of San Francisco vs. Des Moines uses the Mercator projection, which distorts the size of regions near the poles.
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