How to calculate OEE, with a worked example

OEE is overall equipment effectiveness: availability multiplied by performance multiplied by quality. It tells you what share of the possible good output you actually got from a machine. Here is the full arithmetic from one shift, because that is where people get stuck.

The three parts

• •Availability: run time divided by planned production time
• •Performance: what you actually made divided by what you could have made in that run time
• •Quality: good pieces divided by total pieces made

A worked example from one shift

An eight-hour shift is 480 minutes. There is a 30 minute planned break, so planned production time is 450 minutes.

• •Unplanned stops totalled 47 minutes, so run time is 403 minutes
• •The machine ran 14,200 pieces
• •Ideal cycle time is 1.6 seconds per piece
• •Of those, 13,910 were good and 290 were scrap or rework

Now the three numbers.

• •Availability: 403 divided by 450 equals 0.896
• •Performance: 14,200 pieces at 1.6 seconds is 22,720 seconds, or 378.7 minutes of ideal run. 378.7 divided by 403 equals 0.940
• •Quality: 13,910 divided by 14,200 equals 0.980
• •OEE: 0.896 times 0.940 times 0.980 equals 0.825, so 82.5 percent

The sense check that catches most errors

OEE also equals good pieces times ideal cycle time, divided by planned production time. Here: 13,910 times 1.6 seconds is 22,256 seconds, which is 370.9 minutes. Divided by 450 minutes gives 0.824. The two routes agree, so the arithmetic holds.

If your two routes disagree, the usual cause is planned production time. Decide what counts as planned downtime and apply it the same way every shift.

Why 85 percent is not a target

The 85 percent figure comes from a set of world-class benchmark components quoted for decades. It is not a target for your machine, and chasing it produces two bad behaviours: quietly moving things into planned downtime, and running faster than the ideal cycle time so performance exceeds 100 percent.

Compare a machine with itself over time. Comparing OEE between different machines, and especially between different plants, is close to meaningless, because the definition of planned time will differ.

Never report OEE without its three parts

An OEE of 82.5 percent tells you nothing about what to do. Availability 89.6, performance 94.0, quality 98.0 tells you to go and look at the stops. The single number is for a trend line. The three parts are for a decision.

The loss to chase first

Small stops. Long breakdowns get recorded because somebody has to be called. Two-minute stoppages, several times an hour, are invisible on paper and often the largest single loss on a line. If your stop data has no entries under five minutes, the data is wrong rather than the line being good.