The formula
OEE is the product of three factors:
Availability×Performance×Quality=OEE
- Availability = run time ÷ planned production time. It drops with breakdowns, changeovers, waiting for material and any other stop.
- Performance = (ideal cycle time × parts made) ÷ run time. It drops when the machine runs slower than it can: reduced speed and many small stops.
- Quality = good parts ÷ total parts. It drops with scrap and rework.
A worked example
A CNC machine has 480 planned minutes in a shift.
| Downtime (setup, tool change, waiting) | 60 min |
| Run time | 420 min |
| Availability | 420 ÷ 480 = 87.5% |
| Ideal cycle time / parts made | 1.0 min / 360 parts |
| Performance | (1.0 × 360) ÷ 420 = 85.7% |
| Good parts / total parts | 351 / 360 |
| Quality | 351 ÷ 360 = 97.5% |
| OEE | 0.875 × 0.857 × 0.975 = 73.1% |
Example numbers for illustration only.
What is a good OEE?
An OEE of about 85% is often quoted as a world-class benchmark for discrete manufacturing. Plants that have never measured it often find they are well below that, and that most of the gap sits in availability: stops that nobody wrote down. A useful target is not a number from a book but the trend of your own machines, week after week.
How to improve it
- Measure automatically. Manual logs miss short stops and are filled in at the end of the shift. Machine signals give you every second.
- Record a reason for every stop. The biggest loss is rarely the one people expect. Rank the reasons by lost minutes.
- Fix the top reason first. Changeover time, waiting for material and tool changes are common starting points.
- Show the number where people work. A live OEE on the floor changes behaviour faster than a monthly report.
See what your own number could be
The ROI calculator turns the idle share of your machines into hours and money. For the machines on your floor, book a free diagnostic.