What Is Plastic Shrinkage?
Plastic shrinkage is the reduction in material size or volume that can occur as plastic cools and solidifies. It is especially important in injection molding, casting, extrusion, and other manufacturing processes where finished-part dimensions must remain accurate.
This calculator measures volumetric shrinkage—the percentage change between the initial volume and final volume of the material.
How to Use the Plastic Shrinkage Calculator
- Enter the initial volume of the plastic material.
- Enter the final volume after cooling or solidification.
- The calculator returns the plastic shrinkage percentage.
Use the same volume unit for both values, such as cubic centimeters, cubic inches, or cubic meters.
Plastic Shrinkage Formula
Plastic Shrinkage Percentage=(Initial VolumeInitial Volume−Final Volume)×100
Example Calculation
Suppose a plastic component has:
- Initial volume: 200 cm³
- Final volume: 190 cm³
Plastic Shrinkage Percentage=(200200−190)×100=5%
The plastic material has a 5% volumetric shrinkage.
Why Calculate Plastic Shrinkage?
Calculating shrinkage helps manufacturers and designers:
- Plan mold dimensions
- Improve part accuracy
- Compare material behavior
- Reduce defects and rejected parts
- Support quality-control checks
- Evaluate cooling and processing conditions
What Affects Plastic Shrinkage?
Plastic shrinkage can vary depending on:
- Plastic resin type
- Fillers or reinforcements
- Mold temperature
- Cooling rate
- Part thickness
- Packing pressure
- Processing conditions
- Material moisture and curing behavior
Frequently Asked Questions
Does this calculator measure linear mold shrinkage?
No. This calculator measures volume shrinkage from initial and final volumes. Linear mold shrinkage requires length measurements, such as the mold dimension and finished-part dimension.
What units should I use?
Use the same volume unit for the initial and final values. The calculator works with cubic centimeters, cubic inches, cubic feet, cubic meters, or another consistent volume unit.
What does a negative shrinkage result mean?
A negative result means the final volume is larger than the initial volume. This may indicate material expansion, measurement variation, or an incorrect input.
Can I use this calculator for injection molding?
Yes. It can help estimate volumetric shrinkage for injection-molded plastic parts when you know the material volume before and after cooling.
Why does the shrinkage percentage vary between parts?
Shrinkage can change with material type, part geometry, mold temperature, cooling conditions, pressure, and processing settings.
Can I use this calculator for resin or rubber?
Yes. The calculation works for any material when you need to compare initial and final volume. However, the cause of shrinkage may differ between plastics, resins, rubber, and other materials.
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