Enter the inner diameter, outer diameter, and thickness into the calculator to determine the length of the roll of material.

Roll Length Formula

The following formula is used to calculate the length of a roll of material.

L = pi * (OD^2/4 - ID^2/4) / t 
  • Where L is the roll length
  • OD is the outer diameter
  • ID is the inner diameter
  • t is the thickness

A roll length is calculated by multiplying the difference between the diameters squared over 4, by pi, then dividing by the thickness.

Roll Length Definition

A roll length is defined as the length of a material that has been rolled into a cylindrical form with a given material thickness.

Example Problem

How to calculate roll length?

First, determine the outer diameter. For this problem, we are looking at a roll of duct tape that has an outer diameter of 5 inches.

Next, determine the inner diameter. For this example, the duct tape has an inner diameter of 2 inches.

Next, determine the material thickness. On average duct tape has a thickness of .011 inches, so that will be used.

Finally, use the formula to calculate the roll length:

L = pi * (OD^2/4 – ID^2/4) / t

= 3.14159 *(5^2/4 – 2^2/4)/.011

= 1499.39 inches.