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17. How to calculate OEE over multiple shifts?

Q: My boss wants me to calculate and present a graphical OEE representation per week or month. So we need to calculate an average OEE over multiple shifts. I present this as I do with the daily data. I calculate the monthly OEE by taking the average of the daily OEE’s.

Is it alright to present a monthly OEE of the machines by calculating the average of several daily OEE’s in a month?

Arno Koch •  No. Taking 20 OEE numbers, adding them and dividing by 20 does NOT give a correct OEE number. To calculate an OEE over multiple shifts you proceed as follows:

OEE is a Weighted Average of multiple shifts

Since OEE is a weighted average, it is not possible to just average multiple OEE numbers. To calculate OEE over a longer span of time you will need to recalculate the whole equation as if it was one OEE.

How to calculate OEE over multiple shifts?

So calculate the availability over the whole time-span, the performance, the quality and (re)calculate the OEE.

Unfortunately not all OEE software does this correct, leading to wrong conclusions.

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