 Stacey Clark says you should always have your rug sit underneath your sofa and have about 30 to 40% of it all in. You want your rug to ground the space and connect the furniture in a grouping. Also, you want the rug to be wide enough. So in the living room, it should be wider than the sofa. Rugs that are too narrow can throw off the proportions of your room and then sit awkwardly with the furniture.