The size of the coffee table depends on its design and shape. Below I have listed the common sizes for a coffee table of different shapes:  Round or square coffee table: for a medium-size room or your balcony 36 by 36 inches round or oval-shaped coffee table is recommended.  Rectangle shape: the length should be about 40 inches with a width of 30 inches for a small or medium-size room, while for a larger room 48-inches length is ideal with the same width and the height should be about 2 inches smaller than the sofa.