How to calculate OEE

To calculate OEE, work out three factors - Availability, Performance and Quality - and multiply them together. The maths is simple; the hard part is collecting honest data. This guide walks the full method with a worked shift example, then flags the mistakes that quietly inflate the number.

If you're new to the concept, start with what is OEE - this guide assumes you know what the three factors mean and focuses on computing them.

The data you need

Five inputs give you OEE for any window - a shift, a day, a batch:

• Planned production time - scheduled time the line was meant to run (exclude unscheduled time and planned breaks).
• Stop time - total time the line was down during planned time (breakdowns, changeovers, starvation).
• Ideal cycle time - the fastest sustainable time to make one unit (the nameplate rate).
• Total count - all units produced in the window, good and bad.
• Good count - units that met spec the first time, no rework.

Step by step, with a worked example

One 8-hour shift on a single line:

Step 1 - Availability

Run time = planned time − stop time = 480 − 80 = 400 minutes.

Step 2 - Performance

At the ideal cycle time the line could make 24,000 units in 400 minutes of run time. It actually made 19,200.

Equivalently, Performance = (Ideal Cycle Time × Total Count) ÷ Run Time. Performance above 100% means your ideal cycle time is set too slow - fix the standard, don't cap the number.

Step 3 - Quality

Of the 19,200 units, 18,816 were good first time (384 rejects or reworks).

Step 4 - Multiply

Five mistakes that inflate OEE

• Padding planned time. Quietly shrinking scheduled time hides availability loss. Pick one honest definition and stick to it.
• Ignoring small stops and speed loss. If you only log big breakdowns, performance loss vanishes - yet minor stops and slow running are often the biggest hidden cost.
• Counting rework as good. Anything that needed a second pass is a quality loss.
• A too-slow ideal cycle time. Set performance against the real nameplate rate, not a comfortable target, or you'll mask speed loss.
• Manual logging. End-of-shift clipboards miss the short stops entirely and round the rest. Automatic capture is what makes OEE trustworthy.

Once you have a number, the next question is whether it's any good - what is a good OEE score - and where the losses are hiding: the Six Big Losses.