California is about 365 times bigger than Hong Kong.

Hong Kong is approximately 1,108 sq km, while California is approximately 403,882 sq km, making California 36,351% larger than Hong Kong. Meanwhile, the population of Hong Kong is ~7.3 million people (30.0 million more people live in California).
Tip: This to-scale comparison of Hong Kong vs. California uses the Mercator projection, which distorts the size of regions near the poles.