South Dakota is about 8 times bigger than Vermont.

Vermont is approximately 23,956 sq km, while South Dakota is approximately 196,540 sq km, making South Dakota 720% larger than Vermont. Meanwhile, the population of Vermont is ~625,741 people (188,439 more people live in South Dakota).
Tip: This to-scale comparison of Vermont vs. South Dakota uses the Mercator projection, which distorts the size of regions near the poles.