Calculating OEE

The Formulas

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

Availability takes into account Down Time Loss, and is calculated as:

Performance

Performance takes into account Speed Loss, and is calculated as:

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 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

Quality takes into account Quality Loss, and is calculated as:

OEE

OEE takes into account all three OEE Factors, and is calculated as:

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 FactorShift 1Shift 2
Availability90.0%95.0%
Performance95.0%95.0%
Quality99.5%96.0%
OEE85.1%86.6%

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.

ItemData
Shift Length8 hours = 480 min.
Short Breaks2 @ 15 min. = 30 min.
Meal Break1 @ 30 min. = 30 min.
Down Time47 minutes
Ideal Run Rate60 pieces per minute
Total Pieces19,271 pieces
Reject Pieces423 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%

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