Croatia is approximately 56,594 sq km, while United Kingdom is approximately 243,610 sq km, making United Kingdom 330% larger than Croatia. Meanwhile, the population of Croatia is ~4.2 million people (61.5 million more people live in United Kingdom).
This to-scale map shows a size comparison of Croatia compared to United Kingdom. For more details, see an in-depth quality of life comparison of United Kingdom vs. Croatia using our country comparison tool.