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EPEI and batch size calculator
EPEI (every part every interval) is how often a machine that runs several part numbers makes each of them: if every part comes round at least once every two days, the EPEI is two days. A common way to calculate it starts from the time the machine has each day. Take away the production time the demand needs (daily demand × cycle time, added up over the parts) and what is left is the time for changeovers. EPEI = the changeover time for one cycle of all parts ÷ the time left per day, rounded up to an interval you can schedule. The batch size for each part is then its daily demand × EPEI, because each run has to cover the demand until that part comes round again. Page 1 of this template is the calculator sheet: the available time, one row per part with demand, cycle time and changeover, and the results now and with the shorter changeovers you expect after SMED. Page 2 has how to use it, the formulas, what to do when no time is left for changeovers and a worked example. The Excel version takes up to 20 parts, does the sums, rounds the EPEI up to a step you set, flags missing inputs and a machine with no time left, and charts the batch size of each part now and after SMED.
Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.
When to use it
When to use an EPEI and batch size calculator
- When a machine or line shared by several part numbers runs batches set by habit or by the planning system, and nobody knows what its changeovers allow.
- Before a SMED project, to see how much each minute of changeover time is worth in batch size and stock.
- After a SMED project, to reset the batch sizes and the production cycle to the shorter changeovers.
- When demand or the part mix changes, or a part moves to another machine, to check the machine still has time for its changeovers.
How to fill it in
- 1
Work out the available time
Shifts × (minutes per shift − breaks and meetings) − other planned stops, in minutes a day on this machine.
- 2
List the parts
Every part number the machine runs, with its average daily demand, cycle time per piece and the changeover time into that part, from the last good piece of the part before to the first good piece of this one.
- 3
Find the time left for changeovers
Production time per part = daily demand × cycle time ÷ 60. Take the total away from the available time. If nothing is left, stop: the machine cannot make the demand even with no changeovers.
- 4
Work out the EPEI
Add up the changeover times for one cycle of all parts and divide by the time left per day. Round up to an interval you can schedule, such as a shift, a day or a week.
- 5
Size the batches
Batch size = daily demand × EPEI used. Round up to whole containers if the parts move in fixed packs.
- 6
Try the changeovers after SMED
Write the changeover times you expect after SMED and compare the EPEI and the batches. Start the SMED work where the minutes saved shrink the cycle most.
A filled-in example
Illustrative, not a benchmarkAn example: press 4 runs five brackets, BR-10 to BR-50 (illustrative numbers; the rounding step of 1 day is an example value, set your own).
- Available time: 2 shifts × (480 − 30 minutes of breaks) − 20 minutes of other planned stops = 880 minutes a day.
- Daily demand 1,200, 800, 600, 300 and 150 pieces at cycle times of 12, 15, 10, 20 and 24 seconds: production time 240 + 200 + 100 + 100 + 60 = 700 minutes, 79.5% of the available time. 880 − 700 = 180 minutes a day are left for changeovers.
- Changeovers today take 45, 60, 30, 45 and 60 minutes: 240 minutes for one cycle. EPEI = 240 ÷ 180 = 1.33 days, rounded up to 2 days. Batches = demand × 2: 2,400, 1,600, 1,200, 600 and 300 pieces, with 120 minutes of changeovers a day and 60 minutes spare.
- After SMED the changeovers take 20, 25, 15, 20 and 25 minutes: 105 minutes a cycle. EPEI = 105 ÷ 180 = 0.58 days, rounded up to 1 day. Batches = 1,200, 800, 600, 300 and 150 pieces, with 75 minutes spare.
Cutting the changeovers from 240 to 105 minutes a cycle takes the EPEI from 2 days to 1, so every part runs every day and each batch halves: 6,100 pieces a cycle become 3,050. With a half-day step on two shifts, today's 1.33 days could also be rounded to 1.5 days, giving batches of 1,800, 1,200, 900, 450 and 225.
Common mistakes
Using the shift length as the available time
Breaks, meetings and planned stops are not production time. Leave them in and the time left for changeovers looks bigger than it is, and the EPEI comes out too short to keep.
Sizing batches when no time is left
If the production time alone is more than the available time, no batch size will work. Fix the capacity first: cycle time, downtime, more time or another machine.
Keeping the old batch sizes after SMED
Shorter changeovers only reduce stock when the batches and the production cycle are reset to them. Otherwise the saved minutes become idle time.
Trusting a single average
Changeover times that vary a lot, demand that swings by week and minimum batches such as a full coil or a full oven can all push the EPEI up. Check the result on the floor before you commit to it.
Download the template
Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.
Run this template in LeanSuite
In LeanSuite every changeover runs as a digital checklist that logs how long each step took, and Vision AI splits a filmed changeover into internal and external tasks and proposes a shorter sequence.
In the lean glossary
FAQ
EPEI and batch size calculator: common questions
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A shift handover sheet, a red tag log, a changeover checklist for one machine: if your team uses it on the floor, ask.