Montana is about 2.1 times bigger than Cambodia.

Cambodia is approximately 181,035 sq km, while Montana is approximately 376,979 sq km, making Montana 108% larger than Cambodia. Meanwhile, the population of Cambodia is ~16.7 million people (15.7 million fewer people live in Montana).
Tip: This to-scale comparison of Cambodia vs. Montana uses the Mercator projection, which distorts the size of regions near the poles.