Screen size is the size of the viewable screen measured diagonally from the bottom corner to the opposite top corner. Screen size is a very important factor to determine before you purchase your TV. Once you select your screen size, you will narrow down your choices considerably to make your purchase easier. Consider your room size first then determine the screen size based on your room dimensions. People tend to think that bigger is better when it comes to TV's but viewing a large screen in a small room just a few feet away will be really uncomfortable. If your room can't accommodate a large television, it's better to buy a midsize model and leave some space for your furniture. Also keep in mind that the larger screen TV's tend to have more features so if you are looking for options, a small TV may not have enough bells and whistles to keep you happy.