Injection Molding worked example

Plastic Shrinkage with mold cavity dimension of 50 mm: a worked example

Suppose mold cavity dimension falls to 50 mm. This page works the full calculation at that level so you can see exactly which result moves and by how much. Calculate mold shrinkage as a percentage from the mold cavity dimension and the measured molded part dimension.

The inputs for this scenario

  • Mold cavity dimension (steel size): 50 mm (the input this scenario stresses; the baseline uses 100)
  • Molded part dimension (after 24hr conditioning): 98.2 mm (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Shrinkage = ((Cavity dimension - Part dimension) / Cavity dimension) x 100.
  • Rate works out to 50.92 % at these inputs, and this is the headline figure for the scenario.
  • Gap to target works out to -50.92 points at these inputs.
  • Affected count works out to 50 count at these inputs.
  • Total count works out to 98.2 count at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where mold cavity dimension sits at 100 mm and the headline result is 102 %, this scenario comes in 50% below the baseline at 50.92 %.
  • It computes the percentage difference between the steel cavity dimension and the molded part dimension after conditioning. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Rate: 50.92 % (headline result)
  • Gap to target: -50.92 points
  • Affected count: 50 count
  • Total count: 98.2 count

Run it with your numbers

  • To rerun this with your own numbers, open the live Plastic Shrinkage calculator, set mold cavity dimension to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.