Clean the stairs with wood floor cleaner or another appropriate cleaner.
Measure the width of the runner with a ruler. Measure the width of a stair and subtract the runner width from the stair width to center the runner on the stair. For example, if the stair is 30 inches wide and the runner is 25 inches wide, five inches of stair will remain exposed, or 2.5 inches on each side of the runner.
Mark the appropriate measurement from the edge of the stair to edge of the runner on each stair.
Cut two pieces of tackless strip per stair about 1.5 inches narrower than the runner’s width with a pair of scissors.
Install a tackless strip on the surface of the first stair tread 1.5 inches in from the mark you made to center the runner on the stairs. For thinner carpet, place the strip one inch from where the riser meets the tread. For thicker carpet, place the strip up to two inches away. Repeat on all stairs.
Install a tackless strip on the first riser, lining it up with the strip at the back of the tread. Place the strip one to two inches away from where the riser meets the tread, depending on the thickness of the runner. Repeat on all stairs.
Cut a piece of carpet pad for each stair. The width should be the same as the tackless strips and the depth should be long enough butt up against the tackless strip on the back of the tread and wrap over the front edge of the tread known as the “nose.” Staple each pad every six inches until they are secure.
Lay the runner upside-down and ensure a straight edge with a carpenter’s square. Cut the end of the runner with a utility knife if it isn’t already perfectly straight.
Center the runner on the top stair and push up the edge so it’s snug under the nose of the upper landing. Fasten the runner in place with carpet tacks every 4 inches using a tack hammer.
Smooth the runner down until it reaches the bottom of the first riser. Push it tightly into the corner against the tackless strips. Pound the runner into the corner with a blunt chisel along the width.
Smooth the runner down across the stair tread until it reaches the nose. Wrap the runner under the tread nose and secure it with 8 to 12 staples from a staple gun. Repeat this process with all stairs.
Secure the end of the runner at the base of the bottom riser with carpet tacks every four inches as you did on the top stair.