New Zealand is about 1.2 times bigger than Idaho.

Idaho is approximately 214,314 sq km, while New Zealand is approximately 268,838 sq km, making New Zealand 25% larger than Idaho. Meanwhile, the population of Idaho is ~1.6 million people (3.5 million more people live in New Zealand).
Tip: This to-scale comparison of Idaho vs. New Zealand uses the Mercator projection, which distorts the size of regions near the poles.