Industry TemplatesFree referencePDF, Excel, Word exportFoundry

Casting Shrinkage Allowance Table: Pattern Shrink Percent by Alloy

Metal shrinks as it cools from liquid to room temperature, so the pattern must be built larger than the finished casting. This reference table lists typical linear shrinkage allowances by alloy, so designers, pattern makers and buyers can sanity check a shrink rule before cutting a pattern.

Download:
AlloyFamilyLow (%)High (%)Midpoint (%)Approx in per ftApprox mm per m
Gray iron, small section
Cast iron
0.8
1
0.9
0.108
9
Gray iron, heavy section
Cast iron
0.6
0.9
0.75
0.09
7.5
Ductile iron
Cast iron
0.5
1
0.75
0.09
7.5
Malleable iron (as cast white)
Cast iron
1
1.5
1.25
0.15
12.5
White iron
Cast iron
1.5
2
1.75
0.21
17.5
Low carbon steel
Steel
1.6
2.1
1.85
0.222
18.5
Low alloy steel
Steel
1.6
2.1
1.85
0.222
18.5
Austenitic stainless steel
Steel
1.8
2.4
2.1
0.252
21
High manganese steel
Steel
2.2
2.7
2.45
0.294
24.5
Aluminium Al-Si (A356 type)
Aluminium
1
1.3
1.15
0.138
11.5
Aluminium Al-Cu (204 type)
Aluminium
1.2
1.6
1.4
0.168
14
Magnesium alloys
Magnesium
1
1.4
1.2
0.144
12
Yellow brass
Copper alloy
1.3
1.6
1.45
0.174
14.5
Red brass / leaded gunmetal
Copper alloy
1
1.6
1.3
0.156
13
Tin bronze
Copper alloy
1
1.6
1.3
0.156
13
Aluminium bronze
Copper alloy
1.6
2.2
1.9
0.228
19
Copper (cast)
Copper alloy
1.5
2
1.75
0.21
17.5

Typical sand casting ranges for planning only. Actual allowance depends on section thickness, mold rigidity, core restraint and chemistry. Confirm with your foundry and a trial casting, and allow different shrink in different directions for restrained castings. Midpoint conversions use 1 percent equals 0.12 in per ft.

Tooling records in your ERP

Optional: a short review of how patterns, shrink factors and revisions are held in your item master.

Optional. The tool and every export work without this. No spam.

How to use the table

Search for your alloy and read the low and high allowance in percent. The midpoint and the converted values in inches per foot and millimetres per metre give a quick shrink rule size. Multiply a finished dimension by one plus the allowance divided by 100 to get the pattern dimension. For a full per-feature calculation with machining stock, use the pattern allowance worksheet linked on this page.

What affects shrinkage

Shrinkage is not a single constant. Free contraction in a loose sand mold can be higher than in a casting restrained by cores or a rigid flask. Thick sections cool later and may finish contracting differently from thin ones. Graphite expansion in grey and ductile iron offsets part of the contraction, which is why iron allowances are small, whereas steels and aluminium alloys without graphite shrink more. Chemistry, pouring temperature and mold material also move the figure.

  • Restraint from cores reduces effective shrink
  • Heavy sections of iron can show near zero shrink
  • Steels and non-ferrous alloys contract more
  • Different directions may need different allowances

Worked example

A steel bracket is 600 mm long and the foundry uses a 2 percent shrink rule. The pattern length is 600 times 1.02, or 612 mm. The same allowance in a shrink rule is about 0.24 inches per foot. If the casting needs 3 mm of machining stock on each end, add it to the finished length first, then apply the shrink: (600 + 6) times 1.02 equals 618.1 mm. Always apply the allowance to the dimension that includes machining stock.

Common mistakes

Do not copy a table value without checking it against the foundry's own experience. Shrink rules differ between plants. Do not apply shrink to dimensions that are formed by a core print with fixed tolerance, and do not forget that patterns for investment casting and die casting use different tooling shrink logic. In the ERP, store the shrink factor with the pattern or tooling record so revisions are traceable to the casting drawing revision.

Frequently Asked Questions

What is the shrinkage allowance for cast iron?

Grey cast iron is typically around 0.6 to 1.0 percent, and ductile iron about 0.5 to 1.0 percent, because graphite formation expands the metal as it solidifies. Heavy sections can show less. Confirm with your foundry.

What is the shrinkage allowance for steel castings?

Carbon and low alloy steel castings typically use about 1.6 to 2.1 percent, and high manganese or austenitic stainless grades can run higher. Foundries often set a rule per pattern shop.

How do I convert percent to inches per foot?

Multiply the percent by 0.12. For example, 2 percent equals 0.24 inches per foot. For millimetres per metre, multiply the percent by 10.

Do these values include machining allowance?

No. Shrinkage and machining stock are separate. Add machining stock to the finished size, then apply the shrink allowance to that total, as shown in the worked example.

If pattern and tooling data sit outside your ERP, we can help you link shrink factors and drawing revisions to the item master.

Talk to an ExpertExplore More Free Tools

Related Tools

Engineering & PLM

Casting Pattern Allowance Worksheet

Compute pattern dimensions from finished size, machining stock per side and shrink percent, feature by feature, and export the table to Excel.

Industry Templates

Casting Yield Calculator

Calculate casting yield from casting, gating and riser weights, then see the metal you must actually charge per good casting after scrap and melt loss.

Quality & Inspection

Casting Defect Troubleshooting Checklist

A practical checklist of what to check when castings show gas porosity, shrinkage, inclusions, sand defects, cracks or dimensional problems.

Costing & Finance

Foundry Melt Loss Calculator

Convert your melt loss percentage into kilograms, cost per heat and annual cost, then test the saving from improving loss by a few tenths of a point.

More Industry Templates tools

See all
Back to All Tools