North Dakota is about 1.8 times smaller than New Mexico.

New Mexico is approximately 314,310 sq km, while North Dakota is approximately 178,647 sq km, making North Dakota 56.84% the size of New Mexico. Meanwhile, the population of New Mexico is ~2.1 million people (1.4 million fewer people live in North Dakota).
Tip: This to-scale comparison of New Mexico vs. North Dakota uses the Mercator projection, which distorts the size of regions near the poles.