EPEI (Every Part Every Interval) Calculator
EPEI is the interval at which you can produce every part on a shared resource once. It links changeover time, capacity and batch size, and tells you the smallest batch the line can sustain without losing output.
Your numbers
Net of breaks and planned maintenance.
Your results
Planning model with average values. If run time exceeds available time the resource is overloaded and EPEI is shown as 0.
EPEI (days) vs changeover time
Sweeps Average changeover time from 5 to 60, holding your other inputs fixed.
Compute EPEI from ERP routing and demand
An optional conversation about deriving EPEI per work center from your data.
Optional. The tool and every export work without this. No spam.
How to use it
List the part types that share the machine or line, then enter their average changeover time, average daily demand and cycle time per unit. Enter net available time per day. The calculator works out the run time needed per day, the time left for changeovers, and the EPEI in days. It then converts EPEI to a batch per part. If run time exceeds available time, no batching strategy works until capacity or demand changes.
The formula
Total changeover time in one cycle equals parts times average changeover. Capacity left for changeovers per day equals available time minus daily run time. EPEI equals total changeover time divided by that remaining time. A shorter EPEI means smaller batches and less inventory. The batch for each part is daily demand times EPEI. This is the repetitive version of the classic economic batch idea, used in lean to set the production cycle in a mixed model cell.
- EPEI = parts x changeover / (available - run time)
- Batch = daily demand x EPEI
- Cut changeover to cut EPEI
- Averages hide fast and slow movers
Reading the result
An EPEI of one day means you can produce every part daily. Three days means each part runs every three days and you hold safety stock for the gap. The chart shows how steeply EPEI grows with changeover time, which is the business case for SMED. When loading is above about 85 percent, EPEI rises quickly because there is little spare time for setups.
Common mistakes
Using one average for fast and slow parts hides cases where a few high runners should be made every day and the long tail less often. Forgetting scrap, unplanned stops or yield reduces real available time. Use OEE-adjusted available time if possible. Update the ERP lot size rules, such as fixed order quantity or period order quantity, so planning follows the interval you chose.
- Single average for all parts
- Not deducting stops and scrap
- ERP lot size not updated
- Ignoring overloaded resources
Frequently Asked Questions
What is a good EPEI?
Shorter is better. Many plants target one to five days, depending on the product and the cost of changeover. Compare against your replenishment lead time and the variability in demand.
How does EPEI relate to SMED?
Changeover time is in the numerator, so reducing it directly shortens EPEI. SMED is the method, EPEI is the measure that shows whether the improvement pays off in smaller batches.
What if the resource is overloaded?
If run time alone exceeds available time, you need more capacity, less demand, better OEE or an extra shift. Batching changes cannot fix a resource without enough hours.
Should I use average or part-specific data?
Start with averages for a fast estimate, then split into runners, repeaters and strangers. Apply a shorter interval to high-volume parts and a longer one to the tail.
Netray can help pull part-level demand, cycle and setup data from your ERP so EPEI is calculated from real numbers for each resource.
Related Tools
SMED Changeover Reduction Savings Calculator
Turn a setup time reduction target into hours freed, machine cost saved and extra parts per year, with a what-if sweep of the target setup time.
Discrete ManufacturingBatch Size vs Lead Time and Setup Share Calculator
Compare the lead time of a batch through several operations with the share of time lost to setup, and find the batch that reaches a target setup share.
MES & Shop FloorPitch Interval Calculator
Calculate takt time and pitch (takt times pack-out quantity) to set the rhythm of production control and material withdrawal.
MES & Shop FloorLittle's Law WIP and Lead Time Calculator
Turn work in process and daily throughput into average lead time, flow efficiency and the WIP cap needed to hit a lead time goal.