New York City is about 1.6 times smaller than Rio De Janeiro.

Rio De Janeiro is approximately 1,221 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 63.96% the size of Rio De Janeiro.
Tip: This to-scale comparison of Rio De Janeiro vs. New York City uses the Mercator projection, which distorts the size of regions near the poles.