Plastic Shrinkage Calculator
This free plastic shrinkage calculator is the most comprehensive tool on the web. Search 150+ materials, calculate mold dimensions, and compare shrinkage rates instantly. ASTM D955 compliant data trusted by injection molding professionals.
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Mold Dimension Calculator
Calculate required mold cavity size based on desired part dimensions and shrinkage rate
Shrinkage Rate Calculator
Calculate actual shrinkage rate from mold and part measurements
How Our Plastic Shrinkage Calculator Works
This free plastic shrinkage calculator uses ASTM D955 standard data to help engineers and mold designers accurately predict dimensional changes during injection molding. When molten plastic cools from approximately 200-300°C to room temperature, the polymer chains contract—causing shrinkage that must be compensated in mold design.
Our plastic shrinkage calculator provides three powerful tools: a searchable database of 150+ materials with shrinkage rates, a mold dimension calculator that computes required cavity sizes, and a comparison tool for evaluating material alternatives. This data is critical for achieving dimensional accuracy in injection molding. For tool steel selection, use our Brinell to Rockwell hardness calculator.
Crystalline vs Amorphous Plastic Shrinkage
Understanding the difference between crystalline and amorphous polymers is essential when using any plastic shrinkage calculator. The molecular structure fundamentally determines shrinkage behavior:
For tight-tolerance parts in plastic part design, amorphous materials often provide better dimensional control. However, semi-crystalline materials offer superior chemical resistance and fatigue properties that may be required for your application.
Mold Shrinkage Rate Formulas
Our plastic shrinkage calculator uses industry-standard formulas to compute mold dimensions. Here are the key equations used in injection mold design:
Where Dm is the mold cavity dimension, Dp is the desired part dimension, and S is the shrinkage rate percentage. For example, to achieve a 100mm part with 1.5% shrinkage, you need a cavity of 101.5mm.
This reverse calculation helps verify actual shrinkage from measured parts versus mold dimensions. Learn more about optimizing your injection molding tooling projects.
Factors Affecting Plastic Shrinkage Rate
While the plastic shrinkage calculator provides baseline values, actual shrinkage depends on multiple processing factors:
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Plastic Shrinkage Calculator FAQ
Common questions about plastic shrinkage rates and mold design
How accurate is this plastic shrinkage calculator?
Our plastic shrinkage calculator uses ASTM D955 standard values, which represent typical shrinkage ranges under standard processing conditions. Actual shrinkage may vary ±10-20% based on wall thickness, gate location, mold temperature, and packing pressure. For critical tolerances, we recommend test shots with your specific material grade and processing parameters.
Why does my plastic shrink more in one direction than another?
This is called anisotropic shrinkage, and it's especially common with glass-filled materials. Polymer chains and fibers align with flow direction, causing lower shrinkage parallel to flow and higher shrinkage perpendicular to flow. Our plastic shrinkage calculator shows typical ranges, but filled materials may require flow-direction-specific values from your material supplier.
What's the best plastic for low shrinkage parts?
For minimum shrinkage, consider amorphous materials like PC (0.5-0.7%), PMMA (0.2-0.8%), or glass-filled grades. LCP (Liquid Crystal Polymer) offers extremely low shrinkage (0.1-0.5%) for precision applications. Use our plastic shrinkage calculator comparison tool to evaluate options. For tool steel hardness specifications, see our hardness conversion calculator. For help selecting the right material, contact our engineers.
How do I compensate for shrinkage in mold design?
Use the plastic shrinkage calculator's mold dimension tool to scale your cavity dimensions. The formula is: Mold Dimension = Part Dimension × (1 + Shrinkage%/100). For a 100mm part with 2% shrinkage, design a 102mm cavity. Always use the cavity for lower shrinkage tolerance and core for higher—steel is easier to remove than add.
Does this plastic shrinkage calculator work for all materials?
Our database covers 150+ common thermoplastics used in injection molding, including all standard grades of ABS, PC, PP, PE, PA, POM, and engineering resins. Values may vary by manufacturer and grade. For specialty compounds, thermosets, or elastomers, consult your material supplier's technical data sheet for precise shrinkage specifications.
Plastic shrinkage rate reference chart for injection molding materials