OEE is a performance metric and is calculated based on its three contributing factors of availability, performance and Quality. OEE is essentially a ratio of Fully Productive Time to Planned Production time. However it is calculated as the product of its three contributing factors as follows:


1.     Availability is calculated as the ratio of Operating time to planned production time as shown below:

It takes into account down time losses. Down time refers to the amount of time the machine is not available for production. If the production process is down then all other OEE factors are insignificant. Down time losses factor in duration of time lost and the events that lead to this lost time.

Frequent and common causes of downtime loss include:

  • Material shortages.
  • Equipment failures.
  • Changeover time.


Availability of 100% implies the production process is running without any recorded stops.  Collecting data related to downtime losses enables the categorization of the underlying triggering events. A root cause analysis can then be undertaken and the most severe loss events addressed.


2.     Performance is the ratio of Net Operating Time to Operating Time. It is calculated as the ratio of ideal cycle time (minimum cycle time that your process can be expected to achieve in optimal circumstances) to Actual cycle time i.e.:

Performance incorporates Speed Loss. Speed loss refers to any factor that causes the manufacturing process to operate at less than the maximum possible speed or nameplate capacity.


The performance metric will help focus effort in reducing the major causes of speed loss: small stops and reduced speeds.  Tracking the causes of small stops such as misfeeds and products jams can help you train your machine operator to recognize these causes and solve them before they cause a speed loss. Tabulated data on reduced speeds can be analyzed. Such analysis offers great insight into events affecting the state of your machines.


3.     Quality is the ratio of Fully Productive Time to Net Operating Time. It takes into account Quality losses. Quality is practically calculated as the ratio of good pieces to the Total pieces as:


Quality losses refer to pieces that do not meet quality standards. These rejects occur during machine startup and full production runs. Tracking rejects from the machine will aid in identifying underlying causes. These can be monitored and reviewed for insights into the machine state.  Tracking rejects will also help in identifying possible patterns. The Quality metric value can form the basis of a quality control program such as the six sigma program which can be used to focus attention on achieving near perfect quality.


The OEE calculation presented thus far refers to the production process OEE.  Plant OEE can be obtained by using a straight average or a weighted average score of all production processes OEE. Weights can be based on the value added by the production process, focusing on value enhancement. In a plant with three production processes the calculation for straight average would be:

(OEE1 + OEE2 + OEE3) / 3

While that of weighted averages would be:

{(OEE1 x Weight1) + (OEE2 x Weight2) + (OEE3 x Weight3)} / (Weight1 + Weight2 + Weight3)