Croatia is about 4.1 times bigger than Montenegro.

Montenegro is approximately 13,812 sq km, while Croatia is approximately 56,594 sq km, making Croatia 310% larger than Montenegro. Meanwhile, the population of Montenegro is ~604,966 people (3.6 million more people live in Croatia).
Tip: This to-scale comparison of Montenegro vs. Croatia uses the Mercator projection, which distorts the size of regions near the poles.
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