Enter the inside hole diameter, the thickness of the material, and the length of the material into the calculator to determine the outside roll diameter.

Outside Diameter Formula

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

OD = SQRT ( L * t/pi * ID^2/4) * 2
  • Where OD is the outside diameter of the roll
  • L is the length of the roll
  • t is the thickness of the roll
  • ID is the inside diameter (core diameter)

In this case, the units of all values must be the same for the formula to work. For example, if the length is measured/inputted in inches, then the thickness and inner diameter must also be in inches.

Roll Diameter Definition

Roll diameter is a measure of the diameter of the circle created when a material of a certain thickness is rolled into a cylindrical shape.

The thicker and longer the material, the greater the roll diameter will be.

Example Problem

How to calculate outside roll diameter?

First, determine the length of the material being rolled. For this example, the material is found to be 1500 inches long.

Next, determine the thickness of the material. The sheet of material is measured to be .5 inches thick.

Next, determine the inner diameter. In this case, the inner diameter, also known as the core diameter, is calculated to be 3 inches.

Finally, using the formula above, calculate the outside diameter:

OD = SQRT ( L * t/pi * ID^2/4) * 2

OD = SQRT ( 1500 * .5/(3.14159* (3^2/4))) * 2

OD = 20.601 inches