How to Calculate OEE: Formula, Worked Example and Six Big Losses
How to calculate OEE from availability, performance and quality, with a step-by-step worked example and practical ways to act on the result on the line.
OEE (Overall Equipment Effectiveness) measures how much of the time a machine or line was scheduled to produce actually became good product made at the ideal rate. You calculate it by multiplying three factors: OEE = Availability × Performance × Quality. The result tells you how much of your installed capacity you are really using and, more importantly, where the rest is being lost.
Even if a system already reports OEE for your lines, understanding what sits behind the number is what lets you question it, compare lines on equal terms and choose the right improvement.
What OEE measures
OEE compares the time spent producing good units at the standard rate with the time available for production. Because it is built from three sub-indices (availability, performance and quality), it shows not only how far a line is from its potential but also which type of loss is responsible. That makes it a practical tool for evaluating the real use of installed capacity and acting on whatever is holding back delivery.
The last “E” stands for Effectiveness, not Efficiency, a common mix-up. OEE measures the good output a line delivered against the output it could have delivered in the time it was scheduled.
The three OEE factors
| Factor | Formula | Losses it captures |
|---|---|---|
| Availability | Run time ÷ Planned production time | Breakdowns, changeovers, cleaning, line clearance, waiting for material |
| Performance | (Ideal cycle time × Total count) ÷ Run time | Minor stops, slow cycles, running below rated speed |
| Quality | Good count ÷ Total count | Rejects, rework, startup rejects during ramp-up |
Availability
Availability is the share of planned production time during which the equipment actually ran. The gap comes from planned and unplanned stops: changeovers, cleaning, maintenance interventions, breakdowns and waiting for material or instructions.
Performance
Performance compares what was produced with what could have been produced during the run time at the ideal cycle time. It captures speed losses that do not show up as stops: short interruptions, slow cycles and lines deliberately run below rated speed.
Use the ideal cycle time, the fastest rate the equipment can sustain for that product, rather than an average of past results. If the standard already includes the losses, the losses disappear from the indicator.
Quality
Quality is the share of good units in total output. Good units are those that pass the first time, without rework. Rejected and reworked units are losses, including those produced during ramp-up after a changeover.
The OEE formula
The standard formula is:
OEE = Availability × Performance × Quality
Or, in simplified form:
OEE = Fully productive time ÷ Planned production time
where fully productive time = Good count × Ideal cycle time. Both forms give the same result, so the second one is a useful cross-check on the first.
What counts as planned production time
Time when the equipment is not scheduled to run, such as a shift with no production or a plant shutdown, is excluded from planned production time, so it is not an availability loss. Changeovers, cleaning and line clearance between batches stay inside planned production time: they are exactly the losses OEE is designed to expose. Whatever convention you adopt for planned breaks and preventive maintenance, apply it the same way on every line, or comparisons between lines will mislead.
The six big losses
A machine can lose time for countless reasons, but they fall into six classic categories, two for each OEE factor:
- Availability: equipment failures (breakdowns) and setup and adjustments (changeovers, cleaning, line clearance).
- Performance: idling and minor stops, and reduced speed.
- Quality: startup rejects during ramp-up, and production rejects during steady-state running.
Classifying every stop and every reject into one of these categories, and into more specific reasons beneath them, turns OEE from a score into a map of where to act.
A worked example
A machine could run 24 hours a day, but in practice it is scheduled for a 12.5-hour shift. That is its planned production time.
- Availability. During the shift, planned and unplanned stops (a changeover, a maintenance intervention and other interruptions) add up to 2.5 hours. Run time is 10 hours. Availability = 10 ÷ 12.5 = 80%.
- Performance. The ideal cycle time is 1 hour per unit. The machine produced 8 units, which corresponds to a net run time of 8 hours. Performance = 8 ÷ 10 = 80%.
- Quality. Of the 8 units, 2 were rejected. The 6 good units represent 6 hours of fully productive time. Quality = 6 ÷ 8 = 75%.
- OEE = 0.80 × 0.80 × 0.75 = 0.48 = 48%.
Cross-check with the simplified formula: 6 hours ÷ 12.5 hours = 48%.
The breakdown says more than the final number. Of 12.5 scheduled hours, the machine delivered only 6 hours’ worth of good product. The other 6.5 hours split into 2.5 hours of stops, 2 hours of speed loss and 2 hours of quality loss. Because the three losses are of similar size here, no single fix will close the gap.
You can run the same calculation with your own data in the OEE calculator.
What is a good OEE?
An OEE of 85% is commonly cited as world class. It is a useful reference, but only when the definitions behind it match yours. A line with frequent product changeovers and mandatory cleaning carries availability losses that a dedicated high-volume line does not, so compare a line first with its own baseline and with similar lines measured under the same rules. The trend matters more than the absolute value.
Putting OEE to work on the shop floor
Knowing how to calculate OEE is the starting point. The value comes from using the result in the daily routine. Equipment that sits idle or runs below its capacity costs more than it returns and limits the plant’s ability to absorb more demand.
- Find what is taking productive time. A Pareto of losses by reason, line, shift and product shows where the hours go.
- Choose the right lever. Long changeovers call for SMED; recurring breakdowns call for better maintenance planning; waiting time calls for better planning and material flow.
- Feed your improvement routines. Bring OEE data to daily meetings, Kaizen events and SMED workshops, and pair it with structured root cause analysis so actions address causes rather than symptoms.
- Make the data trustworthy. OEE is only as good as the counts and stop reasons behind it. Data captured at the line, automatically and in real time, is easier to act on than end-of-shift recollections.
Applied consistently, the OEE calculation is how you uncover hidden capacity: every improvement that frees productive time increases output from the equipment you already have.
From speedometer to cockpit with Cogtive
OEE tools give you a speedometer; Cogtive, the complete Lean cockpit for manufacturing, gives you the entire cockpit. OEE is the foundation: IoT sensors, AI Vision cameras and batch entries on the tablet feed OEE and the downtime Pareto, alongside maintenance metrics such as MTBF and MTTR and visual management on the floor. On top of that foundation, the Setup pillar attacks changeover losses with Guided Setup and a ramp-up report after each changeover, while the Capacity pillar simulates production scenarios and shows the OEE each one requires. Book a demo to see how your OEE turns into decisions.
The complete Lean cockpit
OEE tools give you a speedometer. Cogtive gives you the entire cockpit.
Setup, capacity, flow and pace in one place, on top of a complete OEE foundation. See it running on a line like yours.
