How to calculate OEE
OEE is calculated as Availability × Performance × Quality. Availability is run time divided by planned production time. Performance is the units actually produced divided by the units the ideal rate would have produced in that run time. Quality is good units divided by total units. A line at 90% on each factor scores 72.9%.
The formula
OEE = Availability × Performance × Quality
- Availability = (Planned Production Time − Downtime) ÷ Planned Production Time
- Performance = (Total Count ÷ Run Time) ÷ Ideal Run Rate
- Quality = Good Count ÷ Total Count
Each factor is a ratio between 0 and 1 (or 0% and 100%). OEE is their product, not their average, so a single weak factor pulls the whole score down.
Source: Augos Executive Summary report
The inputs
Six numbers are enough. Everything else is derived.
| Input | Meaning | Where it comes from |
|---|---|---|
| Shift length | Total time the shift was scheduled | Shift plan |
| Planned stops | Breaks, scheduled cleaning, planned maintenance | Shift plan and standards |
| Downtime | Time the line was stopped inside planned production time | Stop log (operator terminal or manual) |
| Ideal Run Rate | Units per minute the line is designed to produce for this product | Nameplate or product standard |
| Total Count | Every unit produced, good or bad | Pulse sensor or counter |
| Good Count | Units that passed quality | Quality records |
Planned Production Time = Shift length − Planned stops. Run Time = Planned Production Time − Downtime. Note that planned stops are excluded from Availability by design: the operator is not penalised for following the schedule. Augos does still measure them, as Planning Efficiency Loss, because the time scheduled is a loss someone owns.
Worked example
An illustrative eight-hour shift. The figures are chosen to be easy to follow, not taken from a customer.
| Step | Calculation | Result |
|---|---|---|
| Shift length | 8 hours | 480 min |
| Planned stops | Two 15-minute breaks | 30 min |
| Planned Production Time | 480 − 30 | 450 min |
| Downtime | Breakdowns, changeover overrun, waiting | 45 min |
| Run Time | 450 − 45 | 405 min |
| Ideal Run Rate | Nameplate for this product | 60 units/min |
| Total Count | Counted at the line | 21,870 units |
| Good Count | Passed quality | 19,683 units |
Now the three factors:
- Availability = 405 ÷ 450 = 0.900 (90.0%)
- Performance = (21,870 ÷ 405) ÷ 60 = 54 ÷ 60 = 0.900 (90.0%)
- Quality = 19,683 ÷ 21,870 = 0.900 (90.0%)
OEE = 0.900 × 0.900 × 0.900 = 0.729, or 72.9%.
Read it as time: of 450 planned minutes, 45 were lost to stops, another 40.5 were lost to running below ideal speed, and 36.45 were lost to making units that failed quality. The line produced the equivalent of 328 fully productive minutes out of 450.
Simplified formula
If you already know good output and ideal rate, OEE collapses to one line:
OEE = (Good Count × Ideal Cycle Time) ÷ Planned Production Time
In the example: ideal cycle time is 1 second per unit (60 per minute), so 19,683 units × 1 s = 19,683 s = 328.05 min; 328.05 ÷ 450 = 0.729. It gives the same answer and is the quickest way to check a reported OEE, but it hides which factor caused the loss, which is the whole point of decomposing it.
Common mistakes
- Averaging the factors. (90 + 90 + 90) ÷ 3 = 90%, which is wrong. The factors multiply.
- Using a soft ideal rate. If Ideal Run Rate is set to what the line usually does rather than what it is designed to do, Performance reads near 100% and speed loss disappears from view.
- Hiding interruptions in Performance. Interruptions (what standard OEE calls minor stops or micro-stops) are too short to log by hand and depress the speed figure, so a stuttering line looks like a slow one. Measure true speed and report interruptions as their own stop loss, and each shows its own impact.
- Counting planned stops as downtime. Breaks and scheduled cleaning sit outside planned production time. Their overrun against the standard is a loss, but it belongs in Planning Efficiency Loss and Operator Discipline, not in Availability.
- Different formulas on different lines. A manually calculated OEE depends on what was recorded and how. Results from two sites are only comparable if the formula and the inputs are the same.
How Augos calculates it
The Augos platform calculates OEE server-side from measured events: the pulse sensor counts every cycle, the Augos Operator Terminal records each stop and its reason, and quality counts are captured per job. The formula is the one above, applied identically on every line and site, so a shift-on-shift or site-on-site comparison is like for like. Augos then keeps going where standard OEE stops: each lost minute is assigned an owner, and planned stops are measured against their Standard Allowed Time.
Source: Augos Executive Summary report; Augos Factory method
Common questions
What is the OEE formula?
OEE = Availability × Performance × Quality, where Availability is run time divided by planned production time, Performance is actual output divided by the output the ideal rate would give in that run time, and Quality is good units divided by total units.
Why does 90% × 90% × 90% equal 72.9% and not 90%?
Because OEE is the product of three ratios, not an average. Each factor removes a share of what the previous one left, so the losses compound. This is the standard TPM calculation.
How do I calculate OEE in Excel?
Put the six inputs in cells (shift length, planned stops, downtime, ideal run rate, total count, good count), derive planned production time and run time, then multiply the three factor formulas above. The OEE+ calculator does the same arithmetic and adds an owner estimate; its worksheet can be downloaded.
What is Ideal Run Rate and where does it come from?
The nameplate production rate for the line and product, the maximum it is designed to achieve under ideal conditions. It is configuration, not an observation, and should be reviewed when the line's operating standard changes.
What is Ideal Cycle Time?
The reciprocal of Ideal Run Rate: the shortest time the line is designed to take for one unit. At 60 units per minute, ideal cycle time is one second.