Maine is about 4.7 times smaller than Montana.

Montana is approximately 376,979 sq km, while Maine is approximately 79,931 sq km, making Maine 21.2% the size of Montana. Meanwhile, the population of Montana is ~989,415 people (338,946 more people live in Maine).
Tip: This to-scale comparison of Montana vs. Maine uses the Mercator projection, which distorts the size of regions near the poles.