When measuring for a rug for your living room, especially larger rooms with furniture in the middle, be sure the rug is large enough so all the furniture fits entirely on the rug. you can leave about 12"-18" of wood showing.
You can also "teeter" the furniture on your living room rug. Place the front legs of your furniture on the rug and the back legs of your sofa or chairs can be slightly off the rug if desired. You can do this with a smaller rug in a smaller space. Be sure to leave some wood showing.
Smaller sizes such as 5 x 8 area rugs can be placed under a coffee table to define a seating area.
Larges rugs such as 8 x 10, 9 x 12 and 10 x 14 are recommended sizes based on the dimensions of your room.
Make sure you use a quality rug pad to prevent premature wear, indentation from furniture and rug matting.