Injection Molding worked example

Plastic Shrinkage with mold cavity dimension of 250 mm: a worked example

Push mold cavity dimension up to 250 mm and the picture changes. This example computes every intermediate figure at that operating point. Use this to verify actual shrinkage against resin data sheet values, adjust mold cavity dimensions for new resins, or diagnose dimensional issues from process changes.

The inputs for this scenario

  • Mold cavity dimension (steel size): 250 mm (raised for this scenario; the documented default is 100)
  • Molded part dimension (after 24hr conditioning): 98.2 mm (unchanged)

Working through the calculation

  • Applying the documented formula (Shrinkage = ((Cavity dimension - Part dimension) / Cavity dimension) x 100) to the inputs above produces each figure below.
  • At this operating point the engine returns 255 % for rate, the number this scenario is built around.
  • At this operating point the engine returns -255 points for gap to target.
  • At this operating point the engine returns 250 count for affected count.
  • At this operating point the engine returns 98.2 count for total count.

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 150% above the baseline at 255 %.
  • It computes the percentage difference between the steel cavity dimension and the molded part dimension after conditioning. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Rate: 255 % (headline result)
  • Gap to target: -255 points
  • Affected count: 250 count
  • Total count: 98.2 count

Run it with your numbers

  • Every input above is editable in the live Plastic Shrinkage calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.