How to Calculate OEE (Overall Equipment Effectiveness)
Quick answer: OEE measures how much of your planned production time is truly productive. It's the product of three factors — Availability × Performance × Quality. A score of 100% means you're making only good parts, as fast as the equipment can run, with no stop time. World-class OEE is around 85%, and a typical starting point for many plants is closer to 60%.
The Three Factors
| Factor | What it measures | Formula |
|---|---|---|
| Availability | Stop time losses (breakdowns, changeovers) | Run Time ÷ Planned Production Time |
| Performance | Speed losses (slow cycles, minor stops) | (Ideal Cycle Time × Total Count) ÷ Run Time |
| Quality | Defect losses (scrap, rework) | Good Count ÷ Total Count |
A Worked Example
Say a line is scheduled for a 480-minute shift, with 60 minutes of planned stops, so planned production time = 420 minutes.
- Availability: the line ran 380 of those 420 minutes. 380 ÷ 420 = 90.5%.
- Performance: ideal cycle time is 1.0 minute/part and it made 350 parts in 380 run minutes. (1.0 × 350) ÷ 380 = 92.1%.
- Quality: 340 of the 350 parts were good. 340 ÷ 350 = 97.1%.
OEE = 0.905 × 0.921 × 0.971 = about 81%.
What the Score Tells You
The power of OEE isn't the single number — it's that the three factors point to where the loss is. A low Availability says attack downtime and changeovers (see SMED). Low Performance points to speed losses and minor stops. Low Quality points to scrap and rework. OEE turns "the line feels slow" into a measurable, prioritized improvement target.
Common Mistakes
- Comparing OEE across different machines or products as if they're equivalent.
- Inflating the number by excluding losses from "planned" time.
- Chasing OEE % instead of using the factors to remove specific losses.
Frequently Asked Questions
What is a good OEE score?
Around 85% is considered world-class for discrete manufacturing; 60% is common and means significant room to improve. Consistency and trend matter more than a single reading.
Is OEE the same as utilization?
No. Utilization only looks at whether the machine ran. OEE also accounts for how fast it ran and how many good parts it produced.
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