EPEI Calculator: Lot size & Supermarket
EPEI (Every Part Every Interval) tells you how often every variant has to be produced once when a machine has changeover times. The optimal lot size and the required supermarket inventory follow directly from it. Pick an example or calculate from scratch – with a guided calculation path and an explanation of every technical term.
Key figures
Calculated automatically from the machine data and the product mix.
Value stream sketch
A machine with changeover effort produces several variants into a finished-goods supermarket (pull).
Inputs
Machine data and product mix – everything is editable, variants can be added and removed.
Calculation path (guided)
Step by step to the EPEI – with explanations and the current numbers.
Capacity per day
Daily average split – including changeover and the remaining time buffer in the planned cycle.
Machine loading in the cycle
Sequence of the lots over the EPEI interval (run time + changeover). Breaks & stoppages are spread out and not shown here.
Video companion · Questions & answers
All terms and calculation paths from the video – in plain language. Click a question to open the answer. Technical terms are underlined (hover over them).
Key terms explained +
The EPEI metric comes from the Toyota Production System. It answers the question of the economic lot size when a machine has to be changed over – and delivers the matching supermarket inventory at the same time. Here are the most important terms in plain words:
How saving works +
This HTML file is your document. Everything you enter ends up in exactly this file when you save – just like a Word document. If you pass the file on, all calculations in it go with it.
Save (green button or Ctrl+S) stores the current state – without any prompt. As long as no working file of your own has been created, the state is kept in the browser and is there again the next time you open it.
Save as (under “Calculations”) creates a file on your hard drive. This is the only place where you are asked where to save. After that, every further Save writes silently into exactly that file.
The first time: open the file, click “Calculations” and then Save as. From then on the green button is enough.
Saved automatically: as soon as a calculation has been saved once, the tool backs up every further change by itself after a few seconds.
If something goes wrong: the tool continuously keeps an interim state in the browser. If the browser crashes or you close the window by accident, your work is there again the next time you open it.
Note on browsers: writing directly to the file currently works in Chrome and Edge. In Firefox and Safari everything stays saved in the browser – the file itself remains unchanged.