Injection Molding calculator

Plastic Shrinkage Calculator

Calculate plastic shrinkage percentage from mold dimension and molded part dimension. Two counts and a target give you a rate plus how far you are from where you need to be.

What this calculator does

  • Calculate plastic shrinkage percentage from mold dimension and molded part dimension.
  • Use it when plastic shrinkage in injection molding needs a clean rate and gap-to-target you can put on a tier board.
  • Turns plastic shrinkage count, total plastic shrinkage population, target plastic shrinkage rate into a rate for plastic shrinkage in injection molding.

Formula used

  • Plastic shrinkage rate = plastic shrinkage count ÷ total plastic shrinkage population × 100
  • Plastic shrinkage gap to target = plastic shrinkage rate - target plastic shrinkage rate

Inputs explained

  • Plastic shrinkage count: Enter the number of defects, passes, claims, shortages, conforming units, or events being measured.
  • Total plastic shrinkage population: Use the matching inspected, produced, tested, shipped, sampled, or installed population for the same period.
  • Target plastic shrinkage rate: Enter the KPI, specification, contract target, quality target, or internal control limit.

How to use the result

  • Use it when plastic shrinkage in injection molding is being reviewed against a KPI.
  • Trend matters more than a single snapshot; pull the result for the last several periods before you act.

Common questions

  • What problem does this plastic shrinkage calculator solve? Calculate plastic shrinkage percentage from mold dimension and molded part dimension. You get a rate you can defend before quoting, scheduling, or sign-off.
  • Which inputs change the rate the most? plastic shrinkage count, total plastic shrinkage population, target plastic shrinkage rate usually move the rate most. Pull from measured injection molding runs, supplier data, and recent quotes rather than memory.
  • What do I do with this number? Use the gap to target to prioritize the next injection molding kaizen or corrective action.
  • What should I double-check before acting? Confirm the counts came from the same time window and the same scope; mismatched scope is the most common error.

Last reviewed 2026-05-12.