Guam is about 25 times smaller than Montenegro.

Montenegro is approximately 13,812 sq km, while Guam is approximately 544 sq km, making Guam 3.94% the size of Montenegro. Meanwhile, the population of Montenegro is ~604,966 people (435,880 fewer people live in Guam).
Tip: This to-scale comparison of Montenegro vs. Guam uses the Mercator projection, which distorts the size of regions near the poles.
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