A chair rail generally is a length of molding attached to the wall. The height of a chair rail can typically range from 32 inches to 40 inches from the floor. The original purpose of a chair rail was to protect the plaster walls from scrapes and dings made by chairs set against them. Naturally, the molding then was placed to meet the height of the chairs in the home. Where you place your chair rail may be more dependent on aesthetics rather than protection.
Though the chair rail served as protection that was not its only function. The molding, or woodwork, also served to divide the wall into sections. In contemporary design, chair rails are often used to frame panel or wainscoting on the wall. It is then referred to as a dado cap. Other variations of using the chair rail as a decorative divide include separating wallpaper and paint or two paint colors.
Chair rails are typically created from lengths of molding. The profile of the molding can range from a simple curve to an elaborate dentil design. For a chair rail, you want to choose a wall molding, ensuring that the back surface sits flush to the wall. Naturally, the width of the molding should be taken into consideration.
Where you place your chair rail is dependent not only on the height of your ceiling, but also on other architectural features in the room. For example, if you intend to install a chair rail in the kitchen, you may wish to install the chair rail so the top of the molding lines up with the top of your counter. Without such architectural dictates, though, you can use the Golden Mean as your guide for chair rail placement.
Authors Karla J. Neilson and David A. Taylor, in their book "Interiors, an Introduction," define the Golden Mean as "a line that visually divides a wall into two unequal but harmonious parts." The actual mathematical formula for the Golden Mean involves Pi, but for the purposes of interior design, and chair rail placement, the equation is much simpler. If you have 8-foot ceilings, divide 8 by 3. Your answer is 2.6 feet or 30 inches. The bottom of your molding then could be placed at 30 inches above the floor.
This golden rule, though, should be used as a guideline, and not an absolute. If the chairs you intend to line the wall with stand at 36 inches, then center your molding at the 36-inch mark. But if you intend to use the chair rail as a decorative divide, take into consideration the height of your floor molding and crown molding. This reduces the distance and moves your chair rail up slightly. To ensure you get the right aesthetics, run painters tape along the wall one-third of the way up from the floor. Adjust it to suit your taste.
The Golden Mean and rules of thumb (such as the 1/3 distance from the floor) give you a place to start. But what if you have 10-foot ceilings or 15-foot ceilings? Your chair rail would be placed considerably higher and would hardly be considered a chair rail at all. Because a chair rail divides the wall, you need to adapt the rules to your specific needs. But as a rule of thumb, your chair rail is probably going to be most effective, aesthetically and functionally, if you install it between 32 and 40 inches from the floor.