Stair runners are long strips of carpeting that run down the center of a flight of stairs. Underneath the runners are pieces of carpet padding. Both components must be measured and cut properly before considering installation. Since the number of stairs, height and depth of stairs all play a role in proper measurements, it is important to accurately cut all pieces initially.
Measure the width of the stair carpet runner you are using. Note that most stair runners have a standard width to accommodate standard stairs. Subtract two inches from the width of the carpet runner.
Cut each carpet padding strip so its width is 2 inches less than the width of the stair runner.
Measure the depth of one of the stairs from back to front. If needed, cut the padding strips so they are about 1 inch less than this depth.
Measure from about a foot back from the top stair on the top landing. Measure the height from the lip of the top of the stairs to the back of the first stair. This second measurement is the riser height of the stairs.
Measure from the back of the second stair to the lip of the stair where it meets the top of the next riser. This third measurement is the tread (flat section of the stairs) measurement.
Add the riser and tread measurement then multiply this sum by the number of stairs.
Measure from the bottom of the last riser about a foot out on the floor in front of the stairs. Add this measurement and the top landing measurement from Step 4 (the first measurement) to the product of the multiplied amount.
Unroll the carpet runner and measure the length. Cut off any length that exceeds the total measurement from Step 8.