Injection Molding worked example

Runner Weight with runner system volume of 4.25 cc: a worked example

This worked example runs the runner weight numbers for a tougher week than the baseline: runner system volume of 4.25 cc instead of the typical 8.5 cc. Estimate cold runner system weight from runner volume, resin density, and a geometry factor for sprue and sub-runners.

The inputs for this scenario

  • Runner system volume: 4.25 cc (the input this scenario stresses; the baseline uses 8.5)
  • Resin density: 1.04 g/cc (held at the documented default)
  • Geometry/sprue factor: 1.1 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Runner weight = Runner volume x Resin density x Geometry factor.
  • Result works out to 4.86 g at these inputs, and this is the headline figure for the scenario.
  • Basic runner weight (volume x density) works out to 4.86 value at these inputs.
  • Multiplier works out to 1 x at these inputs.
  • Factor A x B works out to 4.42 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where runner system volume sits at 8.5 cc and the headline result is 9.72 g, this scenario comes in 50% below the baseline at 4.86 g.
  • Use it when sizing the shot for a cold-runner mold and when evaluating runner-to-part waste ratios during tool design. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Result: 4.86 g (headline result)
  • Basic runner weight (volume x density): 4.86 value
  • Multiplier: 1 x
  • Factor A x B: 4.42 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Runner Weight calculator, set runner system volume to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.