Enter the final diameter of the tube and the die diameter into the calculator to determine the blow up ratio.

Blow Up Ratio Formula

The following equation is used to calculate a Blow Up Ratio.

BR = Df / Dd
  • Where BR is the Blow Up Ratio
  • Df is the final tube diameter
  • Dd is the die diameter

To calculate a Blow Up Ratio, divide the final tube diameter by the die diameter.

What is Blow Up Ratio?


A blow up ratio is a term used in blown film problems to describe the ratio of the final tube diameter to the die diameter.

How to calculate Blow Up Ratio?

Example Problem:

The following example outlines how to calculate a Blow Up Ratio.

First, determine the diameter of the die. In this example, the die being used is measured to have a diameter of 5 inches.

Next, determine the final tube diameter. The final tube diameter made with this die yields a diameter of 6 inches.

Finally, calculate the Blow Up Ratio using the formula above:

BR = Df / Dd

BR = 6 / 5

BR = 1.2