Chicago is 5 times larger than San Francisco.
Area: 608 km2 calculated
Chicago is the third most populous city in the United States, after New York City and Los Angeles. With 2.7 million residents, it is the most populous city in both the U.S. state of Illinois and the American Midwest. Wikipedia
Area: 122 km2 calculated
San Francisco, officially the City and County of San Francisco, is the cultural center and a leading financial hub of the San Francisco Bay Area and Northern California. Wikipedia