The OEE formula in detail
Availability
Availability measures the proportion of planned production time that the machine was actually running (not stopped due to unplanned failure or unplanned stoppages).
Availability = Run Time ÷ Planned Production Time
Run Time = Planned Production Time − Unplanned Downtime
Example: 480 min planned, 45 min downtime → Run time = 435 min → Availability = 435 ÷ 480 = 90.6%
Performance
Performance compares actual throughput to the maximum possible throughput at ideal speed during the available run time.
Performance = (Total Count ÷ Run Time) ÷ Ideal Run Rate
Example: 180 parts in 435 min, ideal rate 0.5 parts/min → Performance = (180 ÷ 435) ÷ 0.5 = 0.414 ÷ 0.5 = 82.8%
Quality
Quality measures the proportion of total output that meets quality standards (no rework or scrap).
Quality = Good Count ÷ Total Count
Example: 175 good parts from 180 total → Quality = 175 ÷ 180 = 97.2%
OEE
OEE = Availability × Performance × Quality = 90.6% × 82.8% × 97.2% = 72.9%
OEE benchmarks
| OEE score | Rating | Interpretation |
|---|---|---|
| ≥85% | World-class | Excellent — most plants aspire to this level. Only top-quartile manufacturers achieve it consistently. |
| 65–85% | Good | Typical for well-managed manufacturing plants. Room for improvement but not urgently problematic. |
| 40–65% | Average | Typical for most manufacturing plants. Significant losses — likely major opportunities in speed losses and planned downtime. |
| <40% | Unacceptable | Significant, systematic losses. Likely frequent breakdowns and/or severe quality issues. Urgent improvement needed. |
The six big losses
TPM (Total Productive Maintenance) maps OEE losses to six categories that point to the root causes of each component loss:
| OEE component | Loss category | Examples |
|---|---|---|
| Availability | Equipment failure | Breakdown, unplanned stoppages lasting >5 min |
| Setup and adjustment | Changeovers, warm-up, adjustments after changeover | |
| Performance | Idling and minor stoppages | Jams, sensor trips, stoppages <5 min that don't get counted as downtime |
| Reduced speed | Machine running below ideal rate — worn tooling, conservative settings, operator pacing | |
| Quality | Scrap and rework | Defective parts produced during steady-state operation |
| Startup rejects | Defective parts during warm-up or after changeover before process stabilises |
How to improve OEE
The biggest gains typically come from addressing losses in this order:
- Equipment failure (Availability) — usually the biggest single loss. Implement a PdM programme on the top 5 critical pieces of equipment. Each hour of unplanned downtime eliminated has the highest leverage on OEE.
- Minor stoppages and idling (Performance) — often underestimated because they don't appear in downtime records. Install cycle counters and compare to ideal rate — the gap reveals minor stoppages. Address root causes (worn infeed guides, sticky sensors, air blast blockages).
- Reduced speed (Performance) — often operators run below ideal rate due to concern about quality. Identify the root cause of why ideal speed was abandoned and address it.
- Setup and adjustment (Availability) — SMED (Single Minute Exchange of Die) methodology reduces changeover time systematically.
- Scrap and rework (Quality) — use SPC and process capability analysis to identify and eliminate root causes of variation.