Choosing the right size of rug for your room depends on your design objective. A rug can be a focal point or accent. It can unite, extend or separate a room.
5x8 and 6x9 rugs are becoming extremely popular. In many instances, they work interchangeably and give the designer a ton of unique options. In a standard setup, the furniture starts to separate itself from the rug.
10x8 and 12x9 rugs have most, if not all furniture legs on the rug. The purpose of this setup is to define an area. It brings the surrounding furniture together in a cohesive design and separates the area from the rest of the room.
Round rugs work great by mimicking the geometric pattern of round tables as well as many dynamic features in a traditional living room setup.