Figure out the length of a roll of paper by knowing the diameter of the paper roll, the thickness of the paper and the dimension of the centre hole. The stretch or softness of the paper does not factor in to the equation. This knowledge is used to determine how much paper is left on a paper roll or how much carpet is left on a roll of carpet. Another example is figuring out how much fabric is left on a bolt.

Measure the diameter of the paper roll and the centre hole using a tape measure. Write down the measurements.

Use the caliper to measure and write down the thickness of the sheet of paper that is rolled.

Multiply the roll of the diameter by 3.14159. This is the roll circumference in lineal measurements.

Multiply the core diameter by 3.14159. This is the core circumference in lineal measurements.

Add the two answers together and divide by 2. This is the average lap length in lineal measurements.

Subtract the core diameter from the roll diameter. This is the thickness of the roll of paper.

Divide the thickness of the paper by the caliper of the paper. This is the amount of paper layers on the roll.

Multiply the amount of paper layers with the average lap. This is the amount of paper on the roll in lineal measurements.