Modern custom closet systems provide many more organizational options than the standard closet with a rod and a shelf. In spite of the many configuration options available, certain measurement standards--such as the height of the rod--remain.
The standard height for a closet rod is 66 inches from the floor. At this height, long items such as dresses and coats can be hung without touching the floor. There are no standards in terms of length since closet size varies.
Closet rods should be hung 1.5 inches lower than the standard-height shelf, which has the bottom of the shelf at 67.5 inches from the floor. This space allows clearance for hangers. In closets where shelves have been mounted slightly higher or lower than standard height, it's customary to follow suit and hang the rod 1.5 inches below it.
Modern closet systems typically make use of vertical space with the installation of double-hang rods. The top rod is hug at the standard 66 inches and the lower rod is installed 33 inches from the floor. Double-hang rods are meant for shirts, jackets and pants.