Look for the basis weight and basic size of the roll of paper. This should be printed on the specification chart for the roll.
Multiply the basic size's width and length to calculate it's area. As an example, bond paper's basic size is 17 by 22 inches, so it's area is 374 square inches.
Weigh the roll of paper using an appropriately sized weight scale. If this is an industrial roll, it could weigh thousands of pounds.
Measure the width of the roll in inches.
Calculate the linear footage using the formula:
Linear footage = [ ( weight x basic area x 500 ) / (basic weight x width x 12 ) ]
In the example, a 35-inch wide roll of 60-pound bond paper with a roll weight of 1,000 pounds would be calculated as:
Linear footage = [ ( 1,000 x 374 x 500 ) / (60 x 35 x 12 ) ]
Linear footage = 7,420.6 linear feet