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

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 several 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.