What is OEE and how do you calculate it? A plain-language guide

Ask whether a line is "running well" and you usually get two answers. The production manager says the machines are always running; the quality lead says there is too much scrap. Both can be right. OEE (Overall Equipment Effectiveness) brings those two answers together in one number: for how much of your planned time did you produce good parts at the speed you should?

The OEE formula

OEE is the product of three factors:

OEE = Availability × Performance × Quality

• Availability: For how much of the planned production time was the machine actually running? Breakdowns, changeovers and waiting for material bring it down.
• Performance: While it was running, did it run at the speed it should? Small stops and reduced speed bring it down.
• Quality: How many of the parts produced were good the first time? Scrap and rework bring it down.

Because it is a product, OEE is unforgiving. Even if all three factors are 90%, the result is only about 73%. That is why "everything looks fine but OEE is low" is such a common situation.

A step-by-step calculation over one shift

Say you planned an 8-hour shift (480 minutes). There were 47 minutes of stops during the day. The machine's ideal cycle time is 1 minute per part. At the end of the shift you produced 400 parts, of which 12 were scrapped.

There is also an easy way to check your work: multiply the number of good parts by the ideal cycle time and divide by the planned time. (388 × 1) / 480 = 80.8%. If both routes give the same result, your calculation is right.

A word of caution about the 85% target

In discrete manufacturing, an OEE of 85% is often quoted as "world class". The number can be a useful guide, but it varies from industry to industry and from line to line. What matters is not the absolute value but the trend on your own line. Are you improving compared with last month, and which factor holds the biggest loss?

The four most common mistakes

1. Inflating or shrinking planned time. If breaks and planned maintenance are not accounted for, availability drops artificially; the other way round, calling every stop "planned" inflates OEE.
2. Using a loose ideal cycle time. Using the "usual speed" instead of the machine's real capacity hides performance losses.
3. Writing stops down by hand at the end of the shift. Two- or three-minute stops are often never recorded, yet added together they can be the biggest loss of all.
4. Looking at one number and missing the detail. When OEE drops, first check which factor dropped. The fix depends on it: breakdown, setup, material or quality?

Why automatic measurement makes a difference

You can calculate OEE with paper forms, but your data will only ever be as good as the form. When data is collected automatically from the machine's own signals (running, stopped, part counter), three things change:

• Short stops are recorded too, so performance losses become visible.
• The operator only picks the reason for a stop; the calculation happens on its own.
• You see the live status at the line and on your phone without waiting for the end of the shift.

The goal is not a perfect dashboard but data accurate enough to shrink one loss every week.

A short checklist

• Start with a single line, not the whole factory.
• Fix planned time and ideal cycle time in writing.
• Create a short list of stop reasons with no more than 8 to 10 options.
• In the weekly meeting, discuss only the three biggest losses.
• Look at the trend after three months, then move to the second line.