Guide
What is OEE and how to calculate it
OEE (Overall Equipment Effectiveness) shows how much of the planned production time was truly productive. It is the product of three ratios: availability, performance and quality. An OEE of 100% means only good parts, made at the ideal speed, with no stops.
The OEE formula
| Ratio | Formula | What it captures |
|---|---|---|
| Availability | run time ÷ planned production time | losses from stops: breakdowns, changeovers, missing material |
| Performance | (parts × ideal cycle time) ÷ run time | speed losses: slow running, small stops |
| Quality | good parts ÷ total parts | losses from scrap and rework |
Planned production time is the shift length minus planned breaks. Run time is planned time minus downtime. The ideal cycle time is the fastest possible time to make one part on that machine – not the planned rate.
Step-by-step example
An example shift (illustrative numbers, not data from a specific plant):
| Shift length | 8 h = 480 min |
| Planned breaks | 30 min → planned time 450 min |
| Downtime (breakdown, changeover) | 45 min → run time 405 min |
| Ideal cycle time | 30 s (0.5 min per part) |
| Parts produced | 720, of which 700 good |
- Availability = 405 ÷ 450 = 90.0%
- Performance = (720 × 0.5) ÷ 405 = 360 ÷ 405 = 88.9%
- Quality = 700 ÷ 720 = 97.2%
- OEE = 0.900 × 0.889 × 0.972 = 77.8%
Quick check: OEE also equals good parts × ideal cycle time ÷ planned time = 700 × 0.5 ÷ 450 = 77.8%. Both ways must give the same result – if they don't, the data has an error.
What is a good OEE?
A commonly cited "world-class" level is 85%. In practice, comparing with your own baseline matters more than comparing with someone else's number: OEE measured the same way every shift shows whether your actions improve production. Results depend on the industry, the type of machine and how planned time is defined – so when comparing lines, make sure they all calculate OEE by the same rules.
Common mistakes when calculating OEE
- Planned rate instead of ideal cycle time. Performance comes out inflated, sometimes above 100%.
- Data collected by hand at the end of the shift. Short stops and slow running disappear, downtime is rounded, and OEE looks better than reality.
- Inconsistent treatment of breaks. One shift subtracts breaks from planned time, another counts them as downtime – the results can't be compared.
- Missing data counted as downtime. If a counter or the network goes dark, the machine didn't necessarily stop. Periods without data must be marked separately.
- Averaging line OEE without weighting. OEE across lines is combined from times and parts, not by a simple average of percentages.
Measuring OEE automatically
- Every part as an event. A sensor or PLC records each part with an exact timestamp and, where possible, a good/bad result.
- Shift and break calendar in the system, so planned time is calculated for every shift.
- Automatic downtime detection. No part for longer than a set threshold opens a stop; the operator gives the reason.
- Ideal cycle time per product, so performance follows the right rate after a changeover.
That is how BEAT works: it calculates OEE live for every line and shift, splits it into availability, performance and quality, and shows which stops cost the most.
Questions about OEE
What is the difference between OEE and TEEP?
OEE relates losses to planned production time. TEEP relates them to all calendar time (24/7), so it also shows unused shifts and weekends.
Can OEE be above 100%?
Not with correct data. A result above 100% almost always means the ideal cycle time is set too long, for example from the planned rate.
How often should OEE be calculated?
Continuously, summarised per shift. Daily or weekly OEE from manual reports shows a problem only when it is too late to react.
Where should OEE improvement start?
With the biggest loss. Usually one or two downtime reasons dominate – a Pareto of downtime reasons shows where improvement gains the most time.