Six numbers from one shift give you OEE, its three factors, and where the lost minutes went. Nothing is sent anywhere; the math runs in your browser.
Calculator
OEE
76.8%
Biggest loss: availability. 55 minutes of stops.
Availability
87.5%
385 of 440 min running
Performance
89.6%
6,900 parts at 3 s
Quality
98.0%
6,762 good parts
Where the planned time went
Fully productive 338 min
Quality loss 7 min
Performance loss 40 min
Availability loss 55 min
The OEE formula
OEE = Availability × Performance × Quality
Each factor is a ratio, and each one removes a different kind of loss from the time you planned to run.
Availability = Run time ÷ Planned production time
Planned production time is the shift minus breaks. Run time is planned production time minus stop time. Stop time covers unplanned stops, such as breakdowns, and planned stops, such as changeovers.
Performance = (Ideal cycle time × Total count) ÷ Run time
Performance captures slow cycles and small stops. The ideal cycle time is the fastest the process can make one part in the best conditions. If performance comes out above 100%, the ideal cycle time is probably set too slow.
Quality = Good count ÷ Total count
Good count means parts that pass the first time. Reworked parts are not good parts here.
There is also a one-line version that gives the same OEE without the three factors:
OEE = (Good count × Ideal cycle time) ÷ Planned production time
It is correct, but it hides which loss is costing you the most. Use the three factors when you want to know what to fix.
A worked example
One 480-minute shift on a packaging line, with 40 minutes of breaks and 55 minutes of stops. The ideal cycle time is 3 seconds per part. The line made 6,900 parts, and 138 were rejected.
Step
Calculation
Result
Planned production time
480 − 40
440 min
Run time
440 − 55
385 min (23,100 s)
Good count
6,900 − 138
6,762
Availability
385 ÷ 440
87.5%
Performance
(3 × 6,900) ÷ 23,100
89.6%
Quality
6,762 ÷ 6,900
98.0%
OEE
87.5% × 89.6% × 98.0%
76.8%
Three factors that each look healthy still multiply down to 76.8%. That is how OEE behaves: Vorne's own example is that three factors of 90% give only 73%.
What is a good OEE score?
There is no standard. The figure most often quoted as world class is 85%. It goes back to Seiichi Nakajima, who led the introduction of total productive maintenance in Japan in the 1970s and set his numbers as minimums to aim for, from his own experience. Vorne, which runs oee.com, notes that those figures apply to discrete manufacturing, and says most manufacturers score closer to 60%.
Two plants rarely count planned time, stops or ideal cycle time the same way, so their OEE figures are rarely comparable. The useful comparison is the same line against itself last month.
The six big losses
Each factor has two classic losses behind it. They tell you which kind of work will raise the number.
Loss
Lowers
What it is
Equipment failure
Availability
Unplanned stops: breakdowns, tooling failures, waiting for material or operators.
Setup and adjustments
Availability
Planned stops: changeovers, setups and other adjustments.
Idling and minor stops
Performance
Short stops of a minute or two that the operator clears.
Reduced speed
Performance
Running slower than the ideal cycle time.
Process defects
Quality
Scrap and rework during stable production.
Reduced yield
Quality
Scrap and rework from startup until production is stable.
Questions about OEE
What is the OEE formula?
OEE = Availability × Performance × Quality. Availability is run time divided by planned production time. Performance is ideal cycle time multiplied by total count, divided by run time. Quality is good count divided by total count.
How do you calculate OEE in one step?
Multiply the good count by the ideal cycle time and divide by the planned production time. This gives the same OEE figure, but it does not show whether the loss came from stops, slow running or rejects.
What is a good OEE score?
There is no standard. 85% is often quoted as world class, a figure that goes back to Seiichi Nakajima's work on total productive maintenance in Japan. Vorne, which runs oee.com, says most manufacturers score closer to 60%. A target that improves on your own last result is more useful than either number.
Can OEE or performance be over 100%?
Not if the inputs are right. A performance figure above 100% usually means the ideal cycle time is set too slow, so the line appears to beat its own best speed.
Do breaks and changeovers count in OEE?
Breaks, and any other time with no intention to run, are taken out before the calculation: they are not part of planned production time. Changeovers are different. They are planned stops inside production time, so they count as stop time and lower availability.
Do reworked parts count as good?
No. OEE quality counts only parts that pass the first time, the same idea as first pass yield. A part that needs rework is a reject for this calculation.