OEE & Factory Performance worked example

Constraint Buffer Time with buffer inventory ahead of constraint of 2,300 units: a worked example

Suppose buffer inventory ahead of constraint falls to 2,300 units. This page works the full calculation at that level so you can see exactly which result moves and by how much. Estimate protected buffer time from buffer stock and constraint usage.

The inputs for this scenario

  • Buffer inventory ahead of constraint: 2,300 units (the input this scenario stresses; the baseline uses 4,500)
  • Constraint consumption rate: 300 units / hr (held at the documented default)
  • Safety factor: 1.2 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Protected days = inventory on hand ÷ daily usage ÷ safety multiplier.
  • Protected days of supply works out to 6.39 hr at these inputs, and this is the headline figure for the scenario.
  • Unprotected days works out to 7.67 days at these inputs.
  • Inventory works out to 2,300 pieces at these inputs.
  • Daily usage works out to 300 pieces / day at these inputs.

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 48.89% below the baseline at 6.39 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. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Protected days of supply: 6.39 hr (headline result)
  • Unprotected days: 7.67 days
  • Inventory: 2,300 pieces
  • Daily usage: 300 pieces / day

Run it with your numbers

  • To rerun this with your own numbers, open the live Constraint Buffer Time calculator, set buffer inventory ahead of constraint to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.