Municipal Waste Sorting Equipment worked example

Contamination Rate at 5.75% specification or broker target contamination: a worked example

What does the result look like when specification or broker target contamination reaches 5.75%? The full calculation is worked below with real intermediate numbers. Use it when running an ISRI-style bale audit or composition study and you need a clean contamination percentage plus the gap to the spec you ship against.

The inputs for this scenario

  • Out-throw and prohibitive weight in sample: 8 kg (unchanged)
  • Total sampled bale or stream weight: 250 kg (unchanged)
  • Specification or broker target contamination: 5.75 % (raised for this scenario; the documented default is 5)

Working through the calculation

  • Applying the documented formula (Contamination rate = out-throw weight / total sampled weight x 100) to the inputs above produces each figure below.
  • At this operating point the engine returns 3.2 % for contamination rate, the number this scenario is built around.
  • At this operating point the engine returns 2.55 points for gap to specification.
  • At this operating point the engine returns 8 count for out-throw weight.
  • At this operating point the engine returns 250 count for total sampled weight.

How this compares with the baseline

  • Against the tool's baseline example, where specification or broker target contamination sits at 5% and the headline result is 3.2 %, this scenario lands almost exactly on the baseline at 3.2 %.
  • A figure at this level is achievable when specification or broker target contamination is genuinely sustained, not just peaked for a shift. A single sample only represents the bale it came from; contamination varies bale to bale, so trend multiple samples rather than acting on one.

Results at a glance

  • Contamination rate: 3.2 % (headline result)
  • Gap to specification: 2.55 points
  • Out-throw weight: 8 count
  • Total sampled weight: 250 count

Run it with your numbers

  • Every input above is editable in the live Contamination Rate calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.