Mold Shrinkage Calculator

Calculate nominal cavity size from part dimension and linear shrinkage. This practical tool is an engineering estimate—validate decisions against machine, material, mold, and process data.

Formula and method

Cavity dimension = target molded part dimension ÷ (1 − linear shrinkage).

Inputs and units

Enter measured or specified values in the displayed units. Keep units consistent; results are rounded for practical planning. This first release uses the displayed engineering units rather than a unit-switcher.

Worked example

100 mm ÷ (1 − 0.015) = 101.52 mm cavity dimension.

Use this for nominal cavity allowance

Use a shrinkage value defined from the relevant grade and direction. The tool converts a target molded dimension to a first-pass cavity dimension.

What changes the result most

Grade, fillers, orientation, wall thickness, packing, mold temperature, and flow direction.

Common mistake

Applying one isotropic shrinkage value to a fiber-filled or direction-sensitive part.

Interpretation, assumptions, and limitations

This tool provides an estimate for planning and education. It does not replace machine maker limits, material data sheets, mold trials, cavity-pressure data, process validation, or qualified engineering review.

FAQ

Can I use this as a final production setting?

No. Confirm with validated process data and the applicable machine and material documentation.

Why can the real result differ?

Geometry, melt behavior, pressure loss, material lot, temperature, cooling layout, and operating practice can materially affect results.