Idaho is about 1.2 times smaller than New Zealand.

New Zealand is approximately 268,838 sq km, while Idaho is approximately 214,314 sq km, making Idaho 79.72% the size of New Zealand. Meanwhile, the population of New Zealand is ~5.1 million people (3.5 million fewer people live in Idaho).
Tip: This to-scale comparison of New Zealand vs. Idaho uses the Mercator projection, which distorts the size of regions near the poles.