What is OEE?
Overall Equipment Effectiveness (OEE) measures how much of the planned production time is truly productive: making good parts, as fast as possible, with no stops. An OEE of 100% means only good parts, at the ideal speed, with no downtime. It is the key metric of Total Productive Maintenance (TPM) and the most common way to find hidden capacity in a plant before buying new equipment.
The OEE formula
| Factor | Formula | What reduces it |
|---|---|---|
| Availability | Run time ÷ planned production time | Breakdowns, waiting for material, setups and adjustments |
| Performance | (Ideal cycle time × total count) ÷ run time | Small stops, slow cycles, idling |
| Quality | Good count ÷ total count | Startup scrap, rejects and rework |
| OEE | Availability × performance × quality | All of the above |
The six big losses
- Breakdowns: equipment failures and other unplanned stops (availability).
- Setup and adjustment: changeovers, warm-up, adjustments (availability). Cut them with SMED.
- Small stops: short jams, blocked sensors, idling (performance).
- Reduced speed: running slower than the ideal cycle (performance).
- Startup rejects: scrap and rework until the process is stable (quality).
- Production rejects: scrap and rework in steady production (quality).
OEE example
A CNC cell runs an 8-hour shift (480 minutes) with 50 minutes of planned stops, leaving 430 minutes of planned production time. Unplanned stops (39 minutes) and a changeover (35 minutes) leave a run time of 356 minutes: availability 82.8%. At an ideal cycle of 42 seconds, the 452 parts made would take 316 minutes: performance 88.9%. 15 parts were rejected: quality 96.7%. OEE = 82.8% × 88.9% × 96.7% ≈ 71.1%. The waterfall shows the largest losses are unplanned stops (39 minutes), the changeover (35 minutes) and reduced speed (26 minutes).
How to improve OEE
- Measure reliably by shift, with reason codes for every stop.
- Attack the largest loss first; a Pareto chart of stop reasons helps.
- Reduce setups with SMED and breakdowns with autonomous and preventive maintenance.
- Find the causes of small stops at the machine; a gemba walk is a good start.
- Error-proof the process to cut rejects with poka-yoke.
How to use this OEE Calculator tool
- Set the time. Enter the shift or period length and the planned stops (breaks, meetings, planned maintenance).
- List the stops. Add each stop with its reason, category (unplanned stop, setup, small stop) and minutes.
- Enter the counts. Enter the ideal cycle time, the total count and the startup and production rejects.
- Read the result. The tool calculates availability, performance, quality and OEE, compares them with world class and shows the waterfall of the six big losses.
- Attack the biggest loss. The insight shows the largest loss and how much OEE would improve without it.
- Export. Export the OEE report to PDF or Excel, or save it to compare with the next shift.
Frequently asked questions
How do you calculate OEE?
OEE = Availability × Performance × Quality. Availability = run time ÷ planned production time. Performance = (ideal cycle time × total count) ÷ run time. Quality = good count ÷ total count. Equivalently, OEE = (good count × ideal cycle time) ÷ planned production time.
What is a good OEE score?
World-class OEE is usually quoted as 85% (90% availability × 95% performance × 99.9% quality). Typical discrete manufacturers run at 60%, and 40% is common where OEE has never been measured. Trends and the size of each loss matter more than comparing scores between different machines.
What are the six big losses?
The six big losses from Total Productive Maintenance are: breakdowns (unplanned stops) and setup and adjustment (availability losses); small stops and reduced speed (performance losses); startup rejects and production rejects (quality losses).
Are breaks included in OEE?
No. Planned stops such as breaks, meetings and planned maintenance are removed first, leaving planned production time. OEE measures how well that time is used. To include all time, use TEEP (total effective equipment performance), which divides fully productive time by all calendar time.
What is the ideal cycle time?
The ideal cycle time is the theoretical fastest time to produce one unit, usually the nameplate or design speed of the equipment. Using an average or standard time hides speed losses and can push performance above 100%.
What is the difference between OEE and TEEP?
OEE uses planned production time as the base; TEEP uses all time (24 hours a day, 365 days a year). TEEP = OEE × utilization. TEEP shows hidden capacity from extra shifts or days; OEE shows how well the scheduled time is used.