Serbia is about 1.2 times bigger than West Virginia.

West Virginia is approximately 62,361 sq km, while Serbia is approximately 77,474 sq km, making Serbia 24% larger than West Virginia. Meanwhile, the population of West Virginia is ~1.9 million people (4.9 million more people live in Serbia).
Tip: This to-scale comparison of West Virginia vs. Serbia uses the Mercator projection, which distorts the size of regions near the poles.