Ulm is about 7 times smaller than Dallas.

Dallas is approximately 880 sq km, while Ulm (map shows its 55 named neighbourhoods; the area covers the whole city) is approximately 119 sq km, making Ulm 13.49% the size of Dallas.
Tip: This to-scale comparison of Dallas vs. Ulm uses the Mercator projection, which distorts the size of regions near the poles.
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