Calculate plastic shrinkage from original and final length, or determine required mold cavity size from finished dimension and shrinkage percent.

Linear shrinkage is measured relative to the original or mold-cavity dimension. Use grade- and process-specific data for tooling; flow direction, conditioning and molding conditions affect shrinkage.

Related Calculators

Plastic Shrinkage Formula

The following formula is used to calculate the final length of plastic after shrinkage.

FL = OL - (OL × (SP / 100))

Variables:

  • FL is the final length of the plastic (mm)
  • OL is the original length of the plastic (mm)
  • SP is the shrinkage percentage (%)

To calculate the final length of plastic after shrinkage, subtract the product of the original length and the shrinkage percentage divided by 100 from the original length.

What is Plastic Shrinkage?

Plastic shrinkage refers to the reduction in dimensions that occurs when plastic cools and solidifies after being molded. The shrinkage percentage is influenced by the type of plastic, the molding process, and the cooling rate. Accurately predicting shrinkage is crucial for the manufacturing of plastic parts to ensure they meet the desired specifications and fit properly in their intended application.

How to Calculate Plastic Shrinkage?

Select the required solve mode. For final length, enter the original length and a measured or supplier shrinkage percentage. Illustrative material presets are example inputs, not validated grade-specific specifications; verify exact material and process data before tooling.

  1. First, determine the original length of the plastic (OL) in millimeters.
  2. Next, determine the shrinkage percentage (SP) that the plastic will undergo.
  3. Next, gather the formula from above: FL = OL - (OL * (SP / 100)).
  4. Finally, calculate the final length (FL) of the plastic in millimeters.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Original length of the plastic (OL) = 200 mm

Shrinkage percentage (SP) = 2%; the final length is 200 × (1 − 2/100) = 196 mm.