Blow Molding & Hollow Plastic Products worked example

Parison Weight with programmed parison weight per cavity of 31 g: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop programmed parison weight per cavity to 31 g, then walk the calculation through step by step. Estimate total parison resin charge for extrusion blow molded bottles, containers, jerry cans, tanks, or ducts from programmed parison weight, cavity count, and flash allowance.

The inputs for this scenario

  • Programmed parison weight per cavity: 31 g (the input this scenario stresses; the baseline uses 62)
  • Active mold cavities: 4 cavities (held at the documented default)
  • Flash and trim allowance multiplier: 1.12 x (held at the documented default)
  • Unit conversion multiplier: 1 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Parison weight across active cavities = programmed parison weight per cavity × active mold cavities.
  • Total parison resin charge works out to 139 g or lb at these inputs, and this is the headline figure for the scenario.
  • Parison charge before conversion works out to 139 g or lb at these inputs.
  • Unit conversion multiplier works out to 1 x at these inputs.
  • Parison weight across active cavities works out to 124 g or lb at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where programmed parison weight per cavity sits at 62 g and the headline result is 278 g or lb, this scenario comes in 50% below the baseline at 139 g or lb.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to programmed parison weight per cavity, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes a uniform programmed weight across all cavities; on multi-cavity heads with parison-wall-thickness programming differences or unbalanced flow, individual cavity weights can drift and the simple average understates variation.

Results at a glance

  • Total parison resin charge: 139 g or lb (headline result)
  • Parison charge before conversion: 139 g or lb
  • Unit conversion multiplier: 1 x
  • Parison weight across active cavities: 124 g or lb

Run it with your numbers

  • To rerun this with your own numbers, open the live Parison Weight calculator, set programmed parison weight per cavity to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.