Belarus is about 1.2 times bigger than Oklahoma.

Oklahoma is approximately 177,847 sq km, while Belarus is approximately 207,600 sq km, making Belarus 17% larger than Oklahoma. Meanwhile, the population of Oklahoma is ~3.8 million people (5.7 million more people live in Belarus).
Tip: This to-scale comparison of Oklahoma vs. Belarus uses the Mercator projection, which distorts the size of regions near the poles.