The general rule of thumb when hanging a picture over a couch is to choose a piece that is roughly two-thirds the length of the sofa. This results in a balanced and proportional appearance that complements the overall design of the room. However, the exact size of the picture will be determined by the dimensions of the sofa and the amount of wall space available. It is critical to consider the pieces height and width to ensure that it complements the size and style of the room.