Factory handbookH01 · OEE
OEE calculator and guide
OEE (overall equipment effectiveness) is the share of planned production time in which a machine made good parts at full speed. OEE = Availability × Performance × Quality. Enter one shift below and the calculator shows the three factors and where the lost minutes went.
Last reviewed · Deda Systems engineering team, Chennai
Calculator
Calculate OEE for one shift
The figures already in the boxes are the worked example further down. Replace them with your own. Nothing you type leaves your browser.
- Availability
- 88.8%
- Performance
- 88.5%
- Quality
- 97.3%
- OEE
- 76.4%
- Planned production time
- 420 min
- Lost to stops
- 47 min
- Lost to slow running
- 43 min
- Lost to rejects
- 9 min
Formula
The OEE formula
OEE = Availability × Performance × Quality
Availability = Run time ÷ Planned production time
Performance = (Ideal cycle time × Total count) ÷ Run time
Quality = Good count ÷ Total count
| Term | Meaning |
|---|---|
| Planned production time | The time the machine was scheduled to run. Shift length minus planned breaks, meetings and any period with no production planned. |
| Run time | Planned production time minus stop time. Stop time is every stop inside planned time: breakdowns, waiting for material, and setups and changeovers. |
| Ideal cycle time | The fastest time in which the machine can make one part of this product. It is a property of the machine and the part, not the average you achieved. |
| Total count | Every part made in the run time, including rejects. |
| Good count | Parts that were right the first time. A part that needed rework is not a good part for OEE. |
There is a shortcut that gives the same answer: OEE = (Good count × Ideal cycle time) ÷ Planned production time. It is useful as a check, but it hides which of the three factors is causing the loss, which is the whole reason to measure OEE.
Worked example
A worked example
A CNC turning centre runs one 480-minute shift. There are 60 minutes of planned breaks. During the shift the machine is stopped for 47 minutes in total: a changeover, and a wait for material. The ideal cycle time for the part is 90 seconds. The operator makes 220 parts, of which 6 are rejected.
- Planned production time = 480 − 60 = 420 minutes.
- Run time = 420 − 47 = 373 minutes.
- Availability = 373 ÷ 420 = 88.8%.
- Performance = (90 seconds × 220 parts) ÷ 373 minutes = 330 minutes ÷ 373 minutes = 88.5%.
- Quality = 214 ÷ 220 = 97.3%.
- OEE = 88.8% × 88.5% × 97.3% = 76.4%.
The same shift, read as lost time: 47 min lost to stops, 43 min lost to running slower than the ideal cycle or to short stops nobody recorded, and 9 min spent making parts that were rejected. That list tells the owner where to look first. The single percentage does not.
Six big losses
The six big losses
Total Productive Maintenance (TPM) groups everything that pulls OEE down into six losses. Each one belongs to exactly one of the three factors, which is what makes OEE useful for deciding what to fix.
| Loss | OEE factor | What it looks like on the floor |
|---|---|---|
| Equipment failure | Availability | Breakdowns, tool breakage, unplanned maintenance. |
| Setup and adjustments | Availability | Changeovers, first-off approval, waiting for material, an operator or a drawing. |
| Idling and minor stops | Performance | Short stops the operator clears without maintenance: a jam, a sensor, chip clearing. |
| Reduced speed | Performance | Running below the ideal cycle: a reduced feed rate, a worn tool, a cautious operator. |
| Process defects | Quality | Scrap and rework made during steady production. |
| Reduced yield | Quality | Rejects made after start-up or a changeover, before the process settles. |
Where a short stop ends and a breakdown begins is a rule each plant sets for itself. Pick a threshold, write it down and keep it the same from week to week.
Benchmarks
What is a good OEE?
The figure most often quoted is 85%, usually called “world class”. It is attributed to Seiichi Nakajima, who introduced OEE as part of TPM, and his book Introduction to TPM: Total Productive Maintenance (English edition, Productivity Press, 1988). The conditions given were availability above 90%, performance above 95% and quality above 99%. Multiplied together those come to about 84.6%.
Treat it with care. It described award-winning plants in discrete manufacturing, it is decades old, and it is not a pass mark. A job shop with many changeovers and a dedicated line making one part should not be judged against the same number.
Two comparisons are more useful than any benchmark: the same machine against itself last month, and the three factors against each other, because the lowest factor is where the easiest gain usually is.
OEE and TEEP. OEE only counts planned production time. TEEP (total effective equipment performance) counts every hour of the calendar: TEEP = OEE × Utilisation, where utilisation is planned production time divided by all time. A machine at 76% OEE on one shift a day has a much lower TEEP, which is the number to look at before buying another machine. The calculator is on the shop-floor formulas page.
Pitfalls
Common mistakes that inflate OEE
01
Treating changeovers as planned time
If setups are removed from planned production time, availability looks better and the changeover loss disappears from view. Keep setups inside planned time and count them as stops.
02
Using the average cycle time
Performance must be measured against the ideal cycle time. If last month’s average is used as the standard, performance is always close to 100% and tells you nothing.
03
Counting reworked parts as good
Quality in OEE is first-pass. A part that was reworked took machine time twice and belongs in the reject count.
04
Performance above 100%
This means the ideal cycle time on file is slower than the machine can run. Correct the standard instead of reporting the number.
05
Averaging percentages
The OEE of a plant is not the average of its machines’ percentages. Add up the minutes and the counts for all machines, then calculate once.
06
Comparing unlike machines
A press on one part and a VMC on thirty part numbers have different loss profiles. Compare each machine with its own history.
Data
How to collect the data
OEE needs four things per machine per shift: planned time, stop time, total count and reject count, plus an ideal cycle time for each part number. You can start on paper this week.
- On paper. Add start and stop times, a stop reason code and good and reject counts to the job card. Our job card and stop code templates have these fields.
- On a tablet at the machine. The operator taps start, stop and a reason, and the numbers are available during the shift. This is what the paper job cards to live OEE case study describes.
- From the machine. A signal from the controller records run and idle time automatically and the operator only confirms the reason. The options are compared in getting data out of machines.
Sources
Where this comes from
The formulas and definitions on this page are the standard published ones. These are the references we checked them against. If you find an error, write to deep@deda.systems and we will correct it.
- Seiichi Nakajima, Introduction to TPM: Total Productive Maintenance, Productivity Press, 1988 (English edition). Origin of OEE, the six big losses and the 90 / 95 / 99 conditions.
- ISO 22400-2, Key performance indicators (KPIs) for manufacturing operations management, Part 2: Definitions and descriptions. An international standard that defines manufacturing KPIs including an OEE index. Its time model and terms differ slightly from the convention used on this page.
- Lean Enterprise Institute, Lean Lexicon. Definitions of cycle time and related terms.
FAQ
Questions people ask
What is the formula for OEE?
OEE = Availability × Performance × Quality. Availability is run time divided by planned production time. Performance is ideal cycle time multiplied by total count, divided by run time. Quality is good count divided by total count.
Is 85% OEE a realistic target?
85% is a commonly quoted figure attributed to Seiichi Nakajima’s work on TPM, based on 90% availability, 95% performance and 99% quality. It described specific high-performing plants and is not a universal target. Comparing a machine with its own history is more useful.
Do breaks and lunch count against OEE?
No. Planned breaks are removed from planned production time, so they do not reduce OEE. Changeovers and waiting for material happen inside planned time and do count, as availability loss.
Are changeovers an availability loss?
Yes. Setup and adjustment is one of the six big losses and reduces availability. Leaving changeovers out makes OEE look better and hides the time that quick-changeover work could recover.
What is the difference between OEE and TEEP?
OEE measures performance during planned production time. TEEP measures it against all calendar time, 24 hours a day and 7 days a week. TEEP = OEE × Utilisation.
Can OEE be more than 100%?
Not if the inputs are right. A result above 100% almost always means the ideal cycle time is set too slow, so performance is overstated.
Also see
Related pages
H02
Shop-floor formulas
Standard shop-floor formulas, each with a worked example and a calculator: takt time, first pass yield, DPMO, Cp and Cpk, MTBF, MTTR and TEEP.
The factory handbook
A free reference for people who run small and mid-sized plants: an OEE calculator, shop-floor formulas, machine data collection, job card templates and a glossary.
Next step
Want these numbers live?
Everything on this page can be done on paper. When you want it captured at the machine and on a screen during the shift, that is what we build. Thirty minutes on a call is usually enough to tell whether it is worth doing.
- 30 min
- Free first call, with an engineer
- 2–4 days
- On your floor before any proposal
- Week 1
- First working demo, on your own data
- Fixed
- Scope, timeline and price, agreed before we build
- Zero
- Existing systems replaced