Things You'll Need
A roll of carpeting sitting in storage contains a specific length of carpet; however, unrolling the carpeting to find out how much remains can be cumbersome and inconvenient. Instead of unrolling the carpet to measure it, perform a few simple measurements and mathematical calculations to measure rolled carpet. The answer you get should be reasonably accurate for determining the amount of carpet left on the roll, although it may not be exact.
Measure the diameter of the carpet roll in inches with the tape measure. Measure the diameter of the hole in the center of the roll in inches. Measure the thickness of the carpet. Write these measurements down.
Find the area of the entire carpet roll and the area of the hole in the center. For example, if the carpet roll is 22 inches, the radius will be 11 inches. Find the area by multiplying 3.14 * 11 ^2 = 379 .94. If the center hole diameter is 6 inches, the radius will be 3 inches. Find the area by multiplying 3.14 * 3 ^2 = 28.26.
Subtract the area of the center hole from the area of the entire roll to find the adjusted area of the carpet. Using the same example, 379.94 - 28.26 = 351.68.
Divide the adjusted area by the thickness of the carpet to find the linear length. Using the same example, divide 351.68 / 1.25 (thickness of carpet) = 281.34 linear inches. Divide the linear inches by 12 to find linear feet -- 281.34 / 12 = 23.45 feet.
Find the area of the carpet rolled on the carpet roll by multiplying the linear feet by the width. For example, if the carpet is 12 feet wide, multiply 23.45 * 12 = 281.4 square feet.
Convert the square foot measurement to square yards, if necessary. Divide 281.4 / 9 = 31.27 square yards.