So you're planning to place carpet down your stairs and you need to know how much to buy for the project? When trying to come up with the right measurement, it isn't that hard to figure. You must remember to measure all the steps, from the top down to the lower level and then across to get the length measurements.
Measure downward, beginning at the top. First, you need to know where you want the carpet to start and end. Use a helper. Have your helper hold the end of the measuring tape (where the carpet will begin) so you can bring it forward on the flat part of the step and down the fall of the step to the crease (where the next step will join).
Write down these measurements. Because it is not easy to curve your tape measure under the stairs all the way down, multiply your stair measurements by the number of stairs you have (if your stairs each measure the same). If not, you will have to measure each one separately, then add them together.
Check the stairs for equal measurements. Measure a second whole step, over and under to the crease. This is to see if you get the same measurements as the first step.
Add room for padding to the total number. Padding may also take up a little bit of slack, so add a couple of inches to your length total just to be safe. Write down this number.
Measure the width of the stairs. With your tape measure, measure from wall to wall or from one end of the longest step across to the other end (if your steps differ in size).
Write down this measurement and add an additional couple of inches to the width, making room for underneath padding. Take both of these measurements with you to have your stair carpet cut.
Be sure to measure every inch that you want covered with carpet. Recheck your measurements. It is always better to buy a little extra, just in case.