Montana is about 1.9 times bigger than Nebraska.

Nebraska is approximately 199,099 sq km, while Montana is approximately 376,979 sq km, making Montana 89% larger than Nebraska. Meanwhile, the population of Nebraska is ~1.8 million people (836,926 fewer people live in Montana).
Tip: This to-scale comparison of Nebraska vs. Montana uses the Mercator projection, which distorts the size of regions near the poles.