New York City is about 4.7 times bigger than Amsterdam.

Amsterdam is approximately 166 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 371% larger than Amsterdam.
Tip: This to-scale comparison of Amsterdam vs. New York City uses the Mercator projection, which distorts the size of regions near the poles.