Plastic Shrinkage Calculator

Calculate mold cavity dimensions from finished part size and material shrinkage rate to ensure correct part dimensions.

Inputs

Part Length

Part Width

Part Depth

Shrinkage Rate

Tab to move between fields

Results

Cavity Length

152.25 mm

≈ 2 credit cards

Cavity Width81.2 mm

Cavity Depth25.38 mm

Length Oversized By2.25 mm

Width Oversized By1.2 mm

Depth Oversized By0.38 mm

Volumetric Shrinkage4.37%

Cavity Volume313.7 cm³

Total Shrinkage3.83

How to Use This Calculator

Enter the desired finished part dimensions (length, width, depth in mm).
Set the material shrinkage rate (%) from the resin datasheet — typically 0.5–3%.
Review cavity dimensions (enlarged by the shrinkage factor) to machine into the tool steel.
Use the length, width, and depth growth values to adjust your CAD cavity model before machining.

How the result changes with Part Length

Part Length	Cavity Length
500	507.5 mm
1,750	1,776.25 mm
3,250	3,298.75 mm
4,500	4,567.5 mm

What each input means

Part Length: Desired finished part length.
Part Width: Desired finished part width.
Part Depth: Desired finished part depth/height.
Shrinkage Rate: Material shrinkage rate (PE: 1.5-3%, PP: 1-2.5%, ABS: 0.4-0.7%, PC: 0.5-0.7%, PA66: 1-2.2%).

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Part Length = 150, Part Width = 80, Part Depth = 25, Shrinkage Rate = 1.5 = 4 input(s) provided
Calculate Cavity Length
Cavity Length
152.25 = 152.25
Calculate Cavity Width
Cavity Width
81.2 = 81.2
Calculate Cavity Depth
Cavity Depth
25.375 = 25.375

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