Plastics Extrusion - Pipe, Film & Profile worked example

Die Swell Allowance with expected extrudate size at die exit of 0.54 in: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop expected extrudate size at die exit to 0.54 in, then walk the calculation through step by step. Calculate the percent allowance between target finished size and expected extrudate swell at the die.

The inputs for this scenario

  • Expected extrudate size at die exit: 0.54 in (the input this scenario stresses; the baseline uses 1.08)
  • Target finished part size: 1 in (held at the documented default)
  • Reference dimension for percent: 1 in (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Allowance = expected extrudate size - target finished size.
  • Die swell allowance works out to -46 % at these inputs, and this is the headline figure for the scenario.
  • Size difference works out to -0.46 value at these inputs.
  • Expected extrudate size works out to 0.54 value at these inputs.
  • Target finished size works out to 1 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where expected extrudate size at die exit sits at 1.08 in and the headline result is 8 %, this scenario comes in 675% below the baseline at -46 %.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to expected extrudate size at die exit, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. Swell is highly sensitive to resin, melt temperature, shear rate, and draw ratio — a percent measured on one condition will not transfer cleanly to a different material or line speed.

Results at a glance

  • Die swell allowance: -46 % (headline result)
  • Size difference: -0.46 value
  • Expected extrudate size: 0.54 value
  • Target finished size: 1 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Die Swell Allowance calculator, set expected extrudate size at die exit to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.