Montana is about 340 times bigger than Hong Kong.

Hong Kong is approximately 1,108 sq km, while Montana is approximately 376,979 sq km, making Montana 33,923% larger than Hong Kong. Meanwhile, the population of Hong Kong is ~7.3 million people (6.3 million fewer people live in Montana).
Tip: This to-scale comparison of Hong Kong vs. Montana uses the Mercator projection, which distorts the size of regions near the poles.