To choose the correct area rug size for a specific room, consider the furniture and layout, and think about the type and size of the room. It is also helpful to think about the main purpose of using a rug in that room.
A good rule of thumb for choosing the right size rug is to make sure it fits the seating area. The rug doesn’t necessarily need to fit the entire room, but make sure it fits the seating area properly. If the area rug doesn’t fit all furniture on top of it, at least try to fit the front legs of the furniture onto the rug. In a dining room, it is best that the rug goes underneath the table and that the chairs are still on top of the rug when they are pulled out. If the room is large, try to find an area rug large enough to fit all or most of the furniture on top of it.
Inversely, a large rug can make a small room look even more compact. In this case, choose a small rug that is only in the center of the room and underneath the coffee table if there is one. In rooms where the furniture is placed along the wall, it is okay if the furniture only covers the rug halfway.