OEE — Overall Equipment Effectiveness is the reference indicator for measuring how well a machine (or a line) exploits its potential. This guide walks through its structure, its calculation and its practical use, with no shortcuts.
The formula
OEE is the product of three factors: Availability × Performance × Quality. It is precisely this decomposition that makes it useful: it doesn't just say "how much" you yield, but "where" you lose.
- Availability = actual production time / planned time. Unplanned stops, setups and changeovers erode this value.
- Performance = actual output / theoretical output at ideal cycle time. This is where slowdowns and micro-stops hide — the hardest losses to see.
- Quality = good parts / total parts. Scrap and rework weigh as much as downtime.
Example: 90% × 85% × 98% ≈ 75% OEE. It looks good, but it means a quarter of the potential is lost — and OEE tells you where: in this case, mostly in performance.
The six big losses
Traditionally, losses are grouped into six categories: breakdowns and unplanned stops; setups and adjustments; micro-stops; reduced speed; startup rejects; process rejects. Mapping your own losses onto these categories is the fastest way to understand where to intervene.
Mistakes to avoid
- Calculating it only after the fact: it describes the past, it doesn't help you react.
- Not coding downtime reasons: without the "why", OEE is a sterile number.
- Ignoring quality in the calculation, getting optimistic values.
- Comparing machines or processes that aren't comparable.
From the number to improvement
OEE is truly worth it when it is timely and granular: measured at the machine, in real time, with reason codes recorded while the context is fresh. Only then does it become a lever of continuous improvement instead of a figure for the monthly meeting. That is the goal VMES45 pursues by making it visible and actionable, even in companies without an IT department.
