Purchase a length of carpet that is at least as long as you want the runner to be. If you want your runner to be four feet long, then purchase four to five feet of carpet. You can buy carpet at hardware stores, carpet shops, or online.
Figure out the desired width of the runner. It can be as wide as you want it, as long as it is at least a foot less wide than the space in which you plan to use the runner. You want at least six inches of floor to be visible on either side.
Flip the carpet upside down and then measure the width for the runner onto the carpet with a measuring tape. Mark the desired width down the length of the carpet with a black permanent marker and a straight edge.
Cut along the line with a carpet cutter or very sharp box knife. If the box knife is not sharp, it will shred the carpet, making the runner look messy.
Install tackless strips on the floor where you want to put the runner. You’ll need a hammer to put these strips into the floor. Another option is to use double-sided, heavy-duty tape on the runner and then, once it's in place, press down to adhere the tape to the floor.