New York City is about 2.1 times bigger than Las Vegas.

Las Vegas is approximately 367 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 113% larger than Las Vegas.
Tip: This to-scale comparison of Las Vegas vs. New York City uses the Mercator projection, which distorts the size of regions near the poles.