Lean Manufacturing & Operations worked example

Lead Time from WIP (Little's Law) with total work-in-process inventory of 500 units: a worked example

What does the result look like when total work-in-process inventory reaches 500 units? The full calculation is worked below with real intermediate numbers. Use this calculator to determine your expected lead time based on current WIP levels and throughput. This helps set realistic delivery promises and quantify the lead time benefit of WIP reduction.

The inputs for this scenario

  • Total work-in-process inventory: 500 units (raised for this scenario; the documented default is 200)
  • Line throughput rate: 50 units/day (unchanged)
  • Time-unit conversion factor: 1 x (unchanged)

Working through the calculation

  • Applying the documented formula (Lead Time = WIP / Throughput x Conversion Factor) to the inputs above produces each figure below.
  • At this operating point the engine returns 10 days for manufacturing lead time, the number this scenario is built around.
  • At this operating point the engine returns 10 value for raw ratio.
  • At this operating point the engine returns 1 x for conversion factor.
  • At this operating point the engine returns 50 value for throughput rate.

How this compares with the baseline

  • Against the tool's baseline example, where total work-in-process inventory sits at 200 units and the headline result is 4 days, this scenario comes in 150% above the baseline at 10 days.
  • A figure at this level is achievable when total work-in-process inventory is genuinely sustained, not just peaked for a shift. Little's Law assumes a stable system where average arrivals equal average departures; during ramp-ups, shutdowns, or runaway WIP growth the instantaneous result will be misleading.

Results at a glance

  • Manufacturing lead time: 10 days (headline result)
  • Raw ratio: 10 value
  • Conversion factor: 1 x
  • Throughput rate: 50 value

Run it with your numbers

  • Every input above is editable in the live Lead Time from WIP (Little's Law) calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.