Slovenia is about 2.8 times smaller than Croatia.

Croatia is approximately 56,594 sq km, while Slovenia is approximately 20,273 sq km, making Slovenia 35.82% the size of Croatia. Meanwhile, the population of Croatia is ~4.2 million people (2.1 million fewer people live in Slovenia).
Tip: This to-scale comparison of Croatia vs. Slovenia uses the Mercator projection, which distorts the size of regions near the poles.
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