As described in World Class OEE, the OEE calculation is based on the three OEE Factors: Availability, Performance, and Quality. Here’s how each of these factors is calculated.
Availability takes into account Down Time Loss, and is calculated as:
- Availability = Operating Time / Planned Production Time
Performance takes into account Speed Loss, and is calculated as:
- Performance = Ideal Cycle Time / (Operating Time / Total Pieces)
Ideal Cycle Time is the minimum cycle time that your process can be expected to achieve in optimal circumstances. It is sometimes called Design Cycle Time, Theoretical Cycle Time or Nameplate Capacity.
Since Run Rate is the reciprocal of Cycle Time, Performance can also be calculated as:
- Performance = (Total Pieces / Operating Time) / Ideal Run Rate
Performance is capped at 100%, to ensure that if an error is made in specifying the Ideal Cycle Time or Ideal Run Rate the effect on OEE will be limited.
Quality takes into account Quality Loss, and is calculated as:
- Quality = Good Pieces / Total Pieces
OEE takes into account all three OEE Factors, and is calculated as:
- OEE = Availability x Performance x Quality
It is very important to recognize that improving OEE is not the only objective. Take a look at the following data for two production shifts.
|OEE Factor||Shift 1||Shift 2|
Superficially, it may appear that the second shift is performing better than the first, since its OEE is higher. Very few companies, however, would want to trade a 5.0% increase in Availability for a 3.5% decline in Quality!
The beauty of OEE is not that it gives you one magic number; it’s that it gives you three numbers, which are all useful individually as your situation changes from day to day. And it helps you visualize performance in simple terms - a very practical simplification.
Example OEE Calculation
The table below contains hypothetical shift data, to be used for a complete OEE calculation, starting with the calculation of the OEE Factors of Availability, Performance, and Quality. Note that the same units of measurement (in this case minutes and pieces) are consistently used throughout the calculations.
|Shift Length||8 hours = 480 min.|
|Short Breaks||2 @ 15 min. = 30 min.|
|Meal Break||1 @ 30 min. = 30 min.|
|Down Time||47 minutes|
|Ideal Run Rate||60 pieces per minute|
|Total Pieces||19,271 pieces|
|Reject Pieces||423 pieces|
|Planned Production Time||= Shift Length - Breaks|
|= 480 - 60|
|= 420 minutes|
|Operating Time||= Planned Production Time - Down Time|
|= 420 - 47|
|= 373 minutes|
|Good Pieces||= Total Pieces - Reject Pieces|
|= 19,271 - 423|
|= 18,848 pieces|
|Availability||= Operating Time / Planned Production Time|
|= 373 minutes / 420 minutes|
|= 0.8881 or 88.81%|
|Performance||= (Total Pieces / Operating Time) / Ideal Run Rate|
|= (19,271 pieces / 373 minutes) / 60 pieces per minute|
|= 0.8611 or 86.11%|
|Quality||= Good Pieces / Total Pieces|
|= 18,848 / 19,271 pieces|
|= 0.9780 or 97.80%|
|OEE||= Availability x Performance x Quality|
|= 0.8881 x 0.8611 x 0.9780|
|= 0.7479 or 74.79%|