Educational explanation, not professional design advice. Last reviewed 24 October 2026. Disclaimer
In plain English
OEE answers a simple question: of the time a machine was supposed to be making parts, how much was really spent making good parts at full speed? A score of 100% means no stops, no slow running and no scrap. Most real machines score much lower, and OEE shows where the lost time goes.
Technical definition
Overall Equipment Effectiveness is the product of three ratios: availability (run time ÷ planned production time), performance (actual output compared with the ideal output in the run time) and quality (good parts ÷ total parts). It was popularised by Seiichi Nakajima as part of Total Productive Maintenance and is defined as a manufacturing KPI in ISO 22400-2.
How it works and where it is used
The three factors capture the “six big losses”: breakdowns and set-ups (availability), minor stops and reduced speed (performance), and start-up rejects and production rejects (quality). Tracking each factor separately tells you what to improve: maintenance and quick changeover for availability, removing small stoppages for performance, process capability for quality.
Formula
OEE = Availability × Performance × Quality
A = run time ÷ planned time P = (ideal cycle time × total count) ÷ run time Q = good count ÷ total count
Equivalent short form: OEE = (good count × ideal cycle time) ÷ planned production time.
Worked example
A shift with 420 min planned time has 47 min of downtime, an ideal cycle of 1 s, and makes 19 271 parts of which 18 848 are good.
- A = 373 ÷ 420 = 88.8%
- P = (1 s × 19 271) ÷ 22 380 s = 86.1%
- Q = 18 848 ÷ 19 271 = 97.8%
- OEE = 0.888 × 0.861 × 0.978 = 74.8% (check: 18 848 × 1 s ÷ 25 200 s = 74.8%)
In the workshop and in practice
OEE is used on bottleneck machines and lines to measure improvement over time, to prioritise maintenance and changeover work, and to check whether capacity problems come from the machine or from scheduling. It is most useful when the data is collected the same way every shift.
Common mistakes and misconceptions
- Using a slow “standard” cycle time. Performance must use the ideal (best achievable) cycle time, or OEE looks better than it is.
- Excluding losses from planned time. Moving set-ups or small stops out of planned time hides them.
- Comparing OEE between different machines or plants without identical definitions.
- Chasing the number instead of the losses. The value of OEE is in the breakdown of where time is lost.
Related calculators
- OEE Calculator — Overall Equipment Effectiveness from availability, performance and quality.
- Cycle Time Calculator — Observed average time per unit from operating time and units completed.
- Cycle Time & Production Capacity Calculator — How many parts per hour, day and week a machine or line can make.
- Scrap Rate, Yield & First Pass Yield Calculator — Scrap rate, yield, rework rate and first pass yield of a process.
Related topics
- Takt Time — The pace at which one unit must be finished to meet customer demand.
References
- ISO 22400-2: Automation systems and integration — Key performance indicators (KPIs) for manufacturing operations management — Part 2: Definitions and descriptions
- S. Nakajima, Introduction to TPM: Total Productive Maintenance, Productivity Press