Silicone Shrinkage Calculator
Estimate mold cavity dimensions for LSR and HCR silicone parts, predict a finished dimension from a known cavity, or calculate actual shrinkage from trial-mold measurements.
Discuss Your Silicone PartCalculate Silicone Shrinkage
Choose a calculation mode, then enter the dimensions and shrinkage data available for your project.
Advanced: add post-cure shrinkage
Advanced: add post-cure shrinkage
How to Use This Silicone Shrinkage Calculator
Use it for early mold sizing, DFM discussions and trial-mold analysis. Final dimensions should be validated with the actual silicone compound and production process.
Start with the final requirement
Enter the dimension required on the cooled, conditioned silicone part rather than assuming the CAD dimension should equal the mold cavity.
Use realistic shrinkage data
Material-supplier data or trial measurements are better than a generic percentage. The LSR and HCR ranges shown here are starting references only.
Validate critical geometry
Sealing lips, ribs, holes, overmold interfaces, thin sections and critical closure dimensions may require local compensation rather than uniform scaling.
Silicone Shrinkage Formula
This calculator defines shrinkage as the dimensional reduction from the mold cavity to the final silicone part. Using that definition, the simplified mold-sizing equation is:
Mold cavity dimension = Target finished dimension ÷ (1 − Shrinkage rate)Example: for a required final dimension of 50.00 mm and expected linear shrinkage of 2.8%:
50.00 ÷ (1 − 0.028) = 51.44 mmNotice that the tooling enlargement percentage is slightly higher than the shrinkage percentage. At 2.8% shrinkage, the inverse scale factor is about 1.028807×, so the cavity is approximately 2.881% larger than the target finished dimension.
Typical Silicone Shrinkage Reference Ranges
For preliminary estimation, NEWTOP's silicone mold-design guidance uses a broad silicone range of about 2–4%, including commonly referenced ranges around 2.5–4.0% for LSR and 1.5–3.0% for HCR. These values should not be treated as fixed shrinkage for every material grade.
| Material / process | Reference range | Useful for | Before final tooling |
|---|---|---|---|
| Liquid Silicone Rubber (LSR) | Approx. 2.5–4.0% | Early DFM and tooling estimates | Confirm exact LSR grade, mold temperature, pressure and post-cure requirement. |
| High Consistency Rubber (HCR) | Approx. 1.5–3.0% | Compression / transfer molding estimates | Validate compound, hardness, filler system, cure system and molding conditions. |
| General silicone rubber | Approx. 2–4% | Concept-stage estimating | Replace generic assumptions with material-specific or trial-mold data. |
Why Actual Silicone Shrinkage Can Differ
A single percentage cannot fully describe every silicone part. Actual dimensional change can be affected by:
- silicone grade, formulation and filler content;
- Shore hardness;
- mold temperature and demolding temperature;
- cavity pressure and molding parameters;
- gate location and material flow direction;
- wall thickness and local geometry;
- insert constraint in silicone overmolding;
- post-curing and conditioning;
- measurement timing, fixture and method.
When a Single Global Scale Factor Is Not Enough
Uniform scaling is useful for relatively simple parts. It becomes less reliable when a component contains thin diaphragms, tall sealing ribs, major wall-thickness transitions, inserts, long flow paths or tightly controlled mating dimensions. These features may require local compensation, steel-safe tooling and dimensional feedback from a mold trial.
For more detail, read How to Control Silicone Shrinkage During Mold Design . For high-volume liquid silicone parts, see NEWTOP's Liquid Silicone Rubber Injection Molding capabilities.
Need a shrinkage review for a real silicone part?
NEWTOP SILICONE is a custom silicone manufacturer supporting product development from material selection and DFM through tooling, molding, quality control and production. We work with LSR and compression-molded silicone parts for consumer, industrial, medical and other precision applications.
- Engineering support for silicone material, hardness and molding-process selection
- Support from product development and tooling through mass production
- Quality-focused manufacturing for custom silicone parts and application-specific requirements
Silicone Shrinkage FAQ
What is a typical shrinkage rate for silicone rubber?
A broad engineering reference is around 2–4%. LSR is often estimated around 2.5–4.0% and HCR around 1.5–3.0%. The actual production value should be based on the selected silicone grade and molding conditions.
Why is the tooling enlargement percentage different from the shrinkage percentage?
Because shrinkage is calculated from the larger cavity dimension. For example, 2.8% shrinkage corresponds to an inverse tooling scale factor of 1 ÷ 0.972 = 1.028807, which is about 2.881% larger than the desired finished dimension.
Does post-curing cause additional silicone shrinkage?
It can. When post-curing is part of the production process, dimensional approval should normally use the fully post-cured and conditioned part. The calculator lets you estimate a separate post-cure shrinkage stage.
Can this calculator replace a silicone mold trial?
No. This tool is intended for engineering estimation and DFM work. Precision production tools should be validated with the actual material, mold, process parameters, post-cure sequence and measurement method.
How do I calculate actual shrinkage from a trial mold?
Select “Measure Shrinkage,” then enter the known mold cavity dimension and measured final part dimension. The equation is: shrinkage = (cavity dimension − final part dimension) ÷ cavity dimension × 100%.