A stair runner is basically long carpets that are installed on the stairs to give a look of symmetry and gracefulness to the stairs. Installing stair runners on the stairs is an effective way to have peace and quiet as children running up and down stairs can get quite noisy. Stair runners can be effective for safety purposes also as polished wooden stairs can be very slippery.
Stair runners are available in 27 inches and 32 inches width which is the normal size of stairs in the houses in the US and sold by linear foot. The material used for stair runners is either wool or synthetic fibers or at times a combination of both. There is a large variety to choose from, from the plain one color to the fancy ones with intricate designs. At times stair runners do not cover the whole width of the stair, 4 inch of wood is visible on both sides with the runner in the middle to gives a classy look. In case of a wider staircase more wood is left uncovered by the runner. The contrast between the color of runner and wood will look good and the pattern of the railing will stand out. Regarding the length of the runner you have many choices, but usually it ends under the bottom tread and on the top it will end at the back of the top tread. For narrow stairs each stair is covered totally like carpeting and it continues right from the bottom landing to the top. There has to be some coordination between the hall carpeting and the stair runner for continuity and symmetry.