Slide a straight-backed chair (such as a dining chair) up against the wall and measure where the top of the chair meets the wall. This is the height where the chair rail is installed, which typically falls around 34 inches high.
Walk to one end of the wall and measure the desired height, marking it with a pencil. Walk to the other end of the wall and do the same.
Stretch a chalk line between the two pencil marks with the help of an assistant. Place a level on top to ensure it is even and then snap the line against the wall to designate the height of the chair rail.
Repeat the measuring and marking process on the other walls in the room.
Walk to one corner of the room and measure the length of one wall using a tape measure. Write down the measurement and then measure each additional wall, writing down the measurement of each as you go. Add up all of the measurements to determine how much chair rail you need for the room.
Turn the first piece of chair rail upside down on a tarp or workbench and apply a 1/4-inch-wide strip of construction adhesive along the top edge and another 1/4-inch-wide strip along the lower edge.
Turn the chair rail so the adhesive faces the wall and press it into place with the left edge against a wall corner. Align the rail directly over the chalk line on the wall.
Insert 1-inch-long finishing nails into the molding every 12 to 24 inches, but leave the nail head exposed by 1/2 inch. This secures the rail to the wall until the adhesive dries.
Continue installing additional sections of chair rail in the same manner, until covering the entire room's perimeter. Cut the railing when needed using a handsaw or a power saw.
Wait two to three hours and then pull out the nails using pliers and discard them. Fill the holes with wood putty and wait until it dries. Sand the putty smooth with a piece of fine-grit sandpaper.