What is OEE and how is it calculated?
The three parts of OEE, a worked example and common mistakes.
What OEE tells you
OEE (Overall Equipment Effectiveness) shows how much of the planned time actually became good product. 100% means producing for all of the planned time, at ideal speed, with no defects.
Its value is being one number: it brings together whether the machine stopped, ran slowly or made scrap. The useful part is that it shows where the number falls.
The three parts
OEE is the product of three ratios:
- Availability = run time / planned production time. Shows the effect of downtime.
- Performance = (ideal cycle × total count) / run time. Shows the effect of slow running and small stops.
- Quality = good count / total count. Shows the effect of scrap and rework.
A worked example
In a 450-minute shift excluding breaks, the machine stops for 45 minutes and runs for 405. Availability is 90%. The ideal cycle is 30 seconds and 700 pieces were made: 350 minutes of work, so performance is 86.4%. Of the 700, 665 are good: quality is 95%. OEE is about 73.9%.
Change the values below to see the result.
OEE73.9%
Figures are examples.
Common mistakes
A few habits make OEE misleading:
- Mixing up planned stops: define clearly what counts as planned time.
- Setting the ideal cycle from the real average: performance rises artificially.
- Entering scrap in bulk at shift end: you cannot see when quality fell.
- Averaging different lines together: the problem line disappears into the average.
From the number to improvement
Measuring OEE is the start. The real gain comes from finding the biggest loss and focusing on it. That needs downtime recorded with its reason, at the moment it happens; a stop remembered at month end is no longer good data.
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