Tanzania is about 2.5 times bigger than Montana.

Montana is approximately 376,979 sq km, while Tanzania is approximately 947,300 sq km, making Tanzania 151% larger than Montana. Meanwhile, the population of Montana is ~989,415 people (62.9 million more people live in Tanzania).
Tip: This to-scale comparison of Montana vs. Tanzania uses the Mercator projection, which distorts the size of regions near the poles.