How is OEE calculated?

What the three losses mean

The three factors measure three kinds of loss. Availability loss is planned run time lost to stops, such as failures, changeovers or waiting for material. Performance loss is running slower than the ideal cycle time. Quality loss is scrap and parts that need rework. Each factor is a ratio:

• A = run time / planned production time
• P = (ideal cycle time × total count) / run time
• Q = good count / total count

Planned stops, such as lunch breaks and scheduled maintenance, are removed from planned production time first. Under this definition they are not losses.

A hypothetical line, step by step

Hypothetical line: planned time 480 minutes, run time 420 minutes, ideal cycle time 30 seconds (0.5 minutes), 760 parts in total, 722 of them good.

• A = 420 / 480 = 0.875
• P = (0.5 × 760) / 420 = 380 / 420 = 0.905
• Q = 722 / 760 = 0.95
• OEE = 0.875 × 0.905 × 0.95 ≈ 0.752, or 75.2 %

As a check, run time and total count cancel in the product, leaving ideal cycle time × good count / planned time = 0.5 × 722 / 480 = 361 / 480 ≈ 0.752. Both routes give the same result.

Common mistakes

The first mistake is counting planned stops as downtime. If lunch and scheduled maintenance stay in planned time, availability looks lower than the machine really is, and the team works on the wrong problem. The second is entering a wrong ideal cycle time. If it is set longer than the true ideal, performance can go above 100 %, which usually signals an input error. The third is counting reworked parts as good. A part that fails the first pass is a quality loss, even if it is repaired and shipped later.

Follow-up questions