New York City is about 2.2 times bigger than Philadelphia.

Philadelphia is approximately 348 sq km, while New York City (including all five boroughs: Manhattan, Brooklyn, Queens, The Bronx, and Staten Island) is approximately 781 sq km, making New York City 124% larger than Philadelphia.
Tip: This to-scale comparison of Philadelphia vs. New York City uses the Mercator projection, which distorts the size of regions near the poles.
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