First, you'll need to determine the size of the grouping. A horizontal picture should be at least 57 inches wide and 58 inches tall, while a vertical picture should be at least 60 inches high. It's also helpful to note that the pictures should be symmetrical, but you should also keep in mind that symmetry is not necessary when grouping pieces. In general, if you hang horizontal and vertical art on the same wall, they will look balanced.
When hanging pictures in groups, consider their size. If the artworks are different sizes, try to hang them so that the vertical center of each is lined up. Ideally, you should hang the larger picture above the smaller one. Then, you should line them up side-by-side or outside of a key piece of furniture, and so on. The corresponding arrangement is called a “gallery wall.”
The next step in grouping art is to determine how high the artworks are. For a gallery wall, the middle point of each picture should be approximately 57 to 60 inches off the floor. Obviously, this will depend on the height of the ceiling and the height of the individual. However, it is important to be flexible, as you may be trying to work around other artwork or a mantelpiece. If you want to hang pictures in a gallery style, trust your gut instinct and don't use a tape measure.