OEE & Factory Performance worked example

Constraint Buffer Time with buffer inventory ahead of constraint of 11,300 units: a worked example

Push buffer inventory ahead of constraint up to 11,300 units and the picture changes. This example computes every intermediate figure at that operating point. Use it when constraint buffer time in oee and factory performance is being sized for a buffer or safety stock review.

The inputs for this scenario

  • Buffer inventory ahead of constraint: 11,300 units (raised for this scenario; the documented default is 4,500)
  • Constraint consumption rate: 300 units / hr (unchanged)
  • Safety factor: 1.2 x (unchanged)

Working through the calculation

  • Applying the documented formula (Protected days = inventory on hand ÷ daily usage ÷ safety multiplier) to the inputs above produces each figure below.
  • At this operating point the engine returns 31.39 hr for protected days of supply, the number this scenario is built around.
  • At this operating point the engine returns 37.67 days for unprotected days.
  • At this operating point the engine returns 11,300 pieces for inventory.
  • At this operating point the engine returns 300 pieces / day for daily usage.

How this compares with the baseline

  • Against the tool's baseline example, where buffer inventory ahead of constraint sits at 4,500 units and the headline result is 12.5 hr, this scenario comes in 151% above the baseline at 31.39 hr.
  • It divides on-hand inventory by daily usage and then by a safety multiplier to give the number of protected days the buffer covers in front of the constraint. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Protected days of supply: 31.39 hr (headline result)
  • Unprotected days: 37.67 days
  • Inventory: 11,300 pieces
  • Daily usage: 300 pieces / day

Run it with your numbers

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

Last reviewed 2026-05-12.