Idaho is about 1.5 times smaller than New Mexico.

New Mexico is approximately 314,310 sq km, while Idaho is approximately 214,314 sq km, making Idaho 68.19% the size of New Mexico. Meanwhile, the population of New Mexico is ~2.1 million people (491,597 fewer people live in Idaho).
Tip: This to-scale comparison of New Mexico vs. Idaho uses the Mercator projection, which distorts the size of regions near the poles.