ShrinkPro Shrinkage Calculator.
Calculate precise mold cavity dimensions for 30+ injection molding resins. Select your material, enter the desired part dimension, and get instant shrinkage compensation values.
Plastic Shrinkage Calculator
Complete material shrinkage
reference table.
Shrinkage rates for 30+ common injection molding resins. Filter by category or search by name.
| Material | Abbreviation | Category | Min % | Typical % | Max % |
|---|
Shrinkage questions,
answered.
How do I calculate plastic shrinkage for injection molding?
Mold Cavity Dimension = Desired Part Dimension x (1 + Shrinkage Rate). For example, a 100 mm part in ABS with 0.6 percent shrinkage needs a 100.6 mm mold cavity. The ShrinkPro calculator runs this math automatically across 30+ specific resin grades.
Does glass fiber reduce plastic shrinkage?
Yes, significantly. Unfilled PA6 shrinks at 0.7 to 1.5 percent. PA6 GF30 (30 percent glass-filled) shrinks at 0.3 to 0.6 percent in the flow direction. The fibers resist polymer contraction but only along their orientation, which causes anisotropic shrinkage.
What is the difference between mold shrinkage and post-mold shrinkage?
Mold shrinkage is what happens before the part leaves the cavity, measured at 24 hours per ASTM D955. Post-mold shrinkage is additional shrinkage over the next days to weeks as stresses relax and crystallization completes. Nylons and acetal show the most post-mold shrinkage (0.2 to 0.5 percent).
How accurate is a plastic shrinkage calculator?
Bulk shrinkage calculations are accurate to within 0.1 to 0.2 percent under controlled process conditions. Directional effects on glass-filled or asymmetric parts can vary by 0.3 to 0.5 percent and require moldflow analysis. For non-critical dimensions, calculator-based sizing is production-ready.
Can shrinkage be different in different parts of the same mold?
Yes. Wall thickness variation, flow length, gate location, and cooling channel layout all create local shrinkage differences. Thick sections shrink more than thin ones in the same part. This is why warpage exists. Family molds with mixed-thickness parts are notoriously hard to balance.
Need a shrink recommendation for a specific grade or a critical tolerance? Ask an engineer. Or explore more free tools.
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