# Every Product Every Interval (EPEI)

Operations · `EPEI` · verification: source checked

EPEI (written EPEx in the text) is the frequency with which the different part numbers assigned to a machine or process are produced. If every part number assigned to a machine is produced once every three days, then EPEx is three days. A small EPEx lets each part number be made in small lots, which minimises inventories in the system.

## Specification

| Property | Value |
|---|---|
| Kind | metric |

## Study notes

- EPEx is stated to be the frequency with which different part numbers are produced in a production process or system.
- Example given: if a machine is changed over in a sequence so that every part number assigned to it is produced every three days, EPEx is three days.
- In general it is good for EPEx to be as small as possible, so that small lots of each part number are produced and inventories in the system are minimised.
- A machine's EPEx depends on its changeover times and on the number of part numbers assigned to it.
- A machine with long changeovers (and large minimum batch sizes) running many part numbers will inevitably have a large EPEx unless changeover times or the number of part numbers can be reduced.
- The document cross-references Heijunka; no entry for Heijunka is available in the reference list.

## Sources

1. [Every Product Every Interval - Lean Enterprise Institute](https://www.lean.org/lexicon-terms/every-product-every-interval/) (accessed 2026-10-25)

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