Weighted OEE: How To Calculate Total Plant OEE

In this post we will present a simple method to calculate a truly weighted OEE, including weighted factors Availability, Performance, and Quality.

The QUICK weighted OEE method:

Recalling our original definition of OEE, we are measuring how effectively our planned production time (net available time) is used to make a quality (saleable) product.  The weighted OEE then is the total time required to make a quality product divided by the total net available time.

From our examples in the “Calculating OEE” post, the following table summarizes the time required to produce quality products ONLY for machines A, B, and C:

1. Machine A:  365 minutes
2. Machine B:  318.75 minutes
3. Machine C:  254.34 minutes

The total time to produce good quality (saleable) products is 938.09 minutes.

The total net available time for the three machines is 1365 minutes (3 * 455 minutes). 

The total weighted OEE for the 3 machines = 938.09 / 1365 = 68.72%

Calculating the Weighted Factors:

A similar process to the one described above can be applied to the individual factors.  It stands to reason that when the individual factors are multiplied together that we should get the same result.  We will use this to check our answer.

Weighted Availability:

Availability measures machine uptime efficiency.  The definition applied to an individual process also applies to the total of all the machines.  Availability is calculated using the formula:

Availability:  Net Operating Time / Net Available Time

From our examples in the “Calculating OEE” post, the following table summarizes the Net Operating Times for machines A, B, and C:

1. Machine A:  423 minutes
2. Machine B:  437 minutes
3. Machine C:  433 minutes

The total Net Operating Time = 1293 minutes.

The total Net Available Time for the three machines is 1365 minutes (3 * 455 minutes). 

The weighted AVAILABILITY for the 3 machines = 1293 / 1365 = 94.73%

Weighted Performance:

Performance measures machine operating time efficiency when compared to the “ideal” cycle or operating time.  The definition applied to an individual process also applies to the total of all the machines.  Performance is calculated using the formula:

Performance:  Ideal Operating Time / Net Operating Time

From our examples in the “Calculating OEE” post, the following table summarizes the Ideal Operating Times for machines A, B, and C:

1. Machine A:  373.33 minutes
2. Machine B:  337.50 minutes
3. Machine C:  267.17 minutes

The total Ideal Operating Time to produce ALL parts = 978 minutes.

The total Net Operating Time for the three machines is 1293 minutes (See Availability Calculations Above). 

The weighted PERFORMANCE for the 3 machines = 978 / 1293 = 75.64%

Weighted Quality:

Quality measures how efficiently the “ideal” operating time is used to produce quality (saleable) products.  Again, the definition applied to an individual process also applies to the total of all the machines.  Quality is calculated using the formula:

Quality:  Ideal Operating Time to Make Quality Parts / Ideal Operating Time

From our examples in the “Calculating OEE” post, the following table summarizes the Ideal Operating Time to produce Quality Parts ONLY for machines A, B, and C:

1. Machine A:  365.00 minutes
2. Machine B:  318.75 minutes
3. Machine C:  254.34 minutes

The total Ideal Operating Time for Good Parts = 938.09 minutes.

The total Ideal Operating Time to produce ALL parts for the three machines is 978 minutes (See Performance Calculations Above). 

The weighted Quality for the 3 machines = 938.09 / 978.0 = 95.92%

Weighted OEE cross check:

Let’s compare the results.  From the calculations above, the results are summarized as follows:

1. Weighted Availability:  94.73%
2. Weighted Performance:  75.64%
3. Weighted Quality:  95.92%

Now, we multiply the individual weighted OEE factors together:

OEE = 94.73% * 75.64% * 95.92% = 68.73%

You will see the result is the same as the Quick check introduced at the start of this post.

In our next post we will show you how to calculate the weighted factors for each individual process and introduce yet another way to confirm the weighted OEE calculation.

We have created a number of Excel spreadsheets that are immediately available for download from our FREE Downloads page or from the Free Downloads widget on the side bar.  These spreadsheets can be modified as required for your application.

If you have any questions, comments, concerns, or suggestions for a future topic, please forward them by e-mail to leanexecution@gmail.com  We look forward to hearing from you and trust this information will get you going.

Until Next Time, STAY Lean!