Carpeting a staircase requires some consideration before the project begins. You need to decide how much of the stair will be covered, whether you will carpet the vertical "fall" of each step or just the horizontal "tread" of the steps and whether you have landings that break up the stairwell. Fortunately, measuring and fitting carpet can be broken down into a series of manageable steps.
Measure the horizontal step or "tread" of the stairs from front to back, down underneath the protruding lip of the stair, if you have them on your staircase. The "lip" refers to the piece of tread that juts out slightly beyond the place where the horizontal tread meets the vertical fall.
Measure the vertical "fall" or "riser" of the stair, from the top to the bottom where it meets the horizontal plane of the next step. Add the "tread" and "fall" measurements together and multiply by the number of stairs you are carpeting.
Check the stairs for equal measurement. Pick another step on your staircase at random and make sure its measurements match the previous measurements. Measure the area of any landings and add that number to your total. If you have landings that separate flights of stairs, treat each set of stairs as a separate staircase. Do not attempt to do a contiguous measurement from top to bottom.
Measure the width of the stairs, from left to right, to ensure that you have the correct fit of carpet running across the stair. Some people opt to only carpet the centre of their stairs. If that is your intention, take only the measurement for the area you want to carpet.
Take these measurements with you to have your carpet cut. Ask the carpet cutter to add on a few extra inches to both measurements just in case.
Lay carpeting underlay on the bottom step, then pull it up along the riser to the next stair.
Press a gripper into the angle between the tread and the vertical riser of the next step. Nail the gripper into place into the corner, taking care not to hit the teeth of your gripper.
Continue up the stairs, adding grippers to the rear bottom angles of each step as you travel up the staircase.
Begin to lay your carpet at the very bottom of the stairwell, making sure that the pattern of the carpet as well as the pile are running in the correct direction.
Staple the bottom of the carpet into the base of the vertical fall on the first step. Pull it up toward the underside of the first tread (or the "lip" of the tread) and staple it securely. Use the knee kicker to push the carpet into the grippers at the rear of each tread. Repeat this process as you work your way up the staircase.
Finish on the top of the staircase by measuring the amount of carpet you will need to cover the last riser, then trimming any excess carpet. Stretch the carpet into place and fasten it under the very top tread with the staple gun.
Generally people do not carpet their landings, but begin the carpeting on the first step down. Likewise, carpet does not need to be laid on the floor of your hallway, but can end at the base of the vertical drop of your first stair. If you have a spiral staircase, measure the depth of the stairs at their widest point when you are taking the horizontal tread measurement. Accuracy in measurement is critical. You will be installing the carpet from the bottom to the top of the stairs. If you wind up with less than you need, you will have a real problem when you get toward the top because seams in the carpet will be very visible. Be sure to pull the carpet tightly before every staple and to make sure the underlay is smooth as well.