New Zealand is about 1.4 times smaller than Montana.

Montana is approximately 376,979 sq km, while New Zealand is approximately 268,838 sq km, making New Zealand 71.31% the size of Montana. Meanwhile, the population of Montana is ~989,415 people (4.1 million more people live in New Zealand).
Tip: This to-scale comparison of Montana vs. New Zealand uses the Mercator projection, which distorts the size of regions near the poles.