Three factors, one scope
OEE is availability multiplied by performance multiplied by 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. All inputs must refer to the same line, shift and product scope. A break excluded from planned production time must not also be counted as downtime within that interval. Document these conventions before comparing shifts or plants.
Define times and counts at the source
Take planned time from the shift calendar, downtime from machine state events, and total and good counts from counters or quality systems. Define how counter resets, rollovers and machine restarts are handled. Store source timestamps separately from ingestion timestamps. Change the ideal cycle time when the product changes; a single cycle time across different products can overstate or understate performance. Reject negative increments unless they represent a documented correction and keep the correction history.
Check a worked example
With 450 planned minutes, 50 minutes of downtime, an ideal cycle of one second, 20,000 total units and 19,000 good units, run time is 400 minutes. Availability is 88.89%, performance is 83.33% and quality is 95%. OEE is approximately 70.37%. If performance exceeds 100%, do not silently clamp it to 100%. Investigate cycle time, count scope and time units. Our calculator flags that combination as inconsistent so a plausible-looking result does not hide bad inputs.
Do not average percentages blindly
A simple average of two shift OEE percentages can mislead when their durations or products differ. Aggregate underlying times and counts; for mixed products, calculate ideal production time for each product and sum it appropriately. High speed should not hide a poor quality rate. Show loss reasons and data coverage alongside OEE in operational reviews. Missing telemetry is not the same as zero production: flag it as a separate data-quality condition and resolve it before reporting an improvement.
Technical references
Check manufacturer documentation for product capabilities. Project steps and examples were prepared by OPC Turkey.