Carpeting your stairs can be expensive, so be sure when you do decide to make the investment that you buy only as much carpet as you need. The best way to do this is to get accurate measurements to help you determine the amount of carpet you'll need. Fortunately, measuring stairs for carpet is relatively simple and requires only basic materials.
Measure the width of the first stair, from end to end. Write down the measurement.
Measure the length of the first stair by placing the end of the flexible measuring tape at the base of the stair, running it up the front of the stair's rise, bending the tape over the stair's edge, then running it along the flat tread of the step until you reach the bottom of the next stair. If your stairs have a lip, ask someone to help you hold the measuring tape down so that you can get an accurate length measurement. Write the measurement down.
Multiply the length by the width, using your calculator. This will give you the area of the stair. Take the area measurement and multiply that by the number of stairs you are going to carpet.
Find the area of any irregular stairs in your staircase using the same method that you did in Steps 1, 2 and 3. Write the area of the irregular stair(s) down.
Add the area of any irregular stairs to the area measurement you arrived at in Step 3. This is the overall area of the stairs.
Divide the measurement (in feet) you arrived at in Step 5 by the number three, using your calculator. The number you get is the number of yards of carpet you will need to purchase. Since carpet is typically sold by the yard, this measurement will make it easy for you to determine the price of your carpet.