Hi, Bernie. If you are going for historical accuracy, you set them at the height of the top of your dining room chairs so they don't bang holes in the wall. Today, they generally are installed between 28 and 36 inches up. One thing that may help you decide is the height of windows or half walls. Figure how you will install the chair rail around features like this and you will have your answer. Don't forget to cope inside corners if you are going to stain. If you are going to paint, mitering and filler is fine.