OEE is one number answering three questions.
Availability, performance and quality — what each measures, who owns it, and why three factors at 90% give 72.9% rather than 90%.
OEE — Overall Equipment Effectiveness — is a single percentage describing how much of the time you intended to produce actually turned into good parts at the intended rate. It is the product of three factors, each answering a different question, and the reason it has survived forty years is that those three questions have three different owners in a plant.
It is also routinely misused, mostly by being quoted as a headline without the split that makes it actionable.
Multiply the three and you get OEE. The multiplication is why the number falls quickly: three factors at 90% each give 72.9%, which surprises plants the first time they see it and is arithmetically unavoidable.
A productivity measure
OEE measures equipment effectiveness against intent. A plant can post excellent OEE while making the wrong parts in the wrong order and missing dispatch entirely.
Comparable between plants by default
Two plants using different time bases produce numbers that cannot be compared and frequently are anyway. Establish the basis first.
A target to maximise
Pushing OEE on a non-constraint machine produces inventory, not throughput. Improve the constraint; measure the rest.
Meaningful as a single number
Sixty per cent from poor availability and sixty from poor performance are unrelated problems with different owners. The split is the useful part.
| Factor | ISO 22400-2 — the standard | MachineWise variant — internal only |
|---|---|---|
| Availability | Actual production time ÷ planned production time | Machine on-time ÷ reporting time |
| Performance / Effectiveness | (Produced quantity × ideal cycle time) ÷ actual production time | Productive time ÷ machine on-time — a time-in-cut proxy |
| Quality | Good quantity ÷ produced quantity | Identical to ISO |
| Needs a maintained standard? | Yes — an ideal cycle time per part | No |
| Comparable to published benchmarks? | Yes | No — treat as your own baseline |
The variant exists because a floor running fifty part numbers a month often has no trustworthy ideal cycle time, and an OEE that cannot be computed until standards are maintained is an OEE that never gets computed. It is useful internally and it is not the ISO definition. Quote the ISO figure externally, and say which one you used.
There is a widely repeated claim that 85% is world class and 60% is average. The 85% figure has a specific origin and a specific set of assumptions behind it, which are examined in world-class OEE. The honest position is that a first measurement on a previously unmonitored Indian floor usually comes in well below what the plant assumed, and that the gap is nearly always unrecorded idle time rather than breakdowns.
That first drop is the most useful thing OEE does. It converts a vague sense that the floor could do better into a ranked list of causes with hours against each — and the hours convert to rupees at your own machine-hour rate, which is the form in which corrective action gets approved.
Measure one machine honestly for a fortnight before setting any target. Targets set against a number nobody has verified produce gaming rather than improvement, and the fastest way to raise OEE on paper is to reclassify losses.
Then publish the split rather than the product, and review it weekly with the people who own each factor. A plant that installs measurement and does not change its Monday meeting has bought reporting. You can work your own figures in the OEE calculator, or see how it is computed continuously on the OEE monitoring page.