Measure the width of the stair treads with a tape measure. Use this measurement minus 4 or 6 inches when selecting the width of the stair runner you wish to use. The smaller width allows you to position it down the center of the staircase with some of the stair tread remaining visible along the sides.
Use chalk to make a mark on each step where you’ll attach the carpet runner using its width.
Measure the depth of each stair tread. Cut a piece of carpet padding measuring 1 inch shorter than the stair depth and runner width using a utility knife. Place the padding on each tread, centered between the carpet runner marks and positioned against the stair riser running along the rear of the tread. Secure it in place using a hammer stapler, placing a staple every 6 inches along the padding.
Place the carpet runner roll on the fourth step from the base of the staircase. Pull lightly on its end until it extends to a point 2 inches beyond the bottom step. Use the runner marks to center it in place.
Secure the runner to the bottom of the riser along the bottom step with the hammer stapler by placing a series of staples 4 to 6 inches apart through the runner and into the step. Make sure the bottom is flush against the floor along the landing.
Mold the carpet tightly to the step riser and place a second line of staples along the bottom of the overhang of the step's tread. Pull the carpet runner tightly over the tread using a knee kicker to place it against the rear of the tread against the next step's riser. Place a row of staples in the corner of the fold between the tread and the riser, and then place a carpet knife at the fold and hammer the carpet between the riser and tread.
Place a line of staples at the base of the second step’s riser, and repeat the carpet placement on the second step with the same installation process. Continue repeating for each additional step until you reach the top of the staircase. Cut the carpet along the fold of the top tread and the final step’s riser using a carpet knife.