Pasadena is about 20 times smaller than Los Angeles.

Los Angeles (including the city proper only) is approximately 1,215 sq km, while Pasadena is approximately 59 sq km, making Pasadena 4.9% the size of Los Angeles.
Tip: This to-scale comparison of Los Angeles vs. Pasadena uses the Mercator projection, which distorts the size of regions near the poles.
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