Casting Shrinkage Allowance Calculator
Work out the pattern dimension needed to allow for solidification shrinkage, so the finished casting comes out to size.
Method
Pattern dimension = casting dimension / (1 − shrinkage%)
Patternmakers add shrinkage so the metal contracts to the target size as it cools.
Typical linear shrinkage
| Alloy | Shrinkage |
|---|---|
| Gray cast iron | 1.0% |
| Ductile iron | 0.8% |
| Carbon steel | 2.0% |
| Stainless steel | 2.1% |
| Aluminum | 1.3% |
| Brass / bronze | 1.5–1.6% |
Frequently Asked Questions
How do I calculate shrinkage allowance?
Divide the casting dimension by (1 − shrinkage fraction). For 100 mm in steel at 2%, the pattern is 100/0.98 = 102.04 mm.
What is patternmaker’s shrinkage?
The extra size added to a pattern so the casting shrinks to the correct final dimension as it solidifies and cools.
How much does cast iron shrink?
About 1.0% for gray iron and 0.8% for ductile iron.
Does shrinkage vary with shape?
Yes, restrained sections shrink less; these are nominal linear values — confirm with first articles.
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