New Mexico is about 5 times smaller than Mongolia.

Mongolia is approximately 1,564,116 sq km, while New Mexico is approximately 314,310 sq km, making New Mexico 20.1% the size of Mongolia. Meanwhile, the population of Mongolia is ~3.2 million people (1.2 million fewer people live in New Mexico).
Tip: This to-scale comparison of Mongolia vs. New Mexico uses the Mercator projection, which distorts the size of regions near the poles.