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

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## 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.