OEE Calculator
Overall Equipment Effectiveness with a full time-loss breakdown.
OEE
77.3%
- Availability
- 90.6%
- Performance
- 88.5%
- Quality
- 96.4%
- Time lost to availability Downtime minutes straight off the shift.
- 45 min
- Time lost to speed Run time minus the time the ideal cycle time would have needed.
- 50 min
- Time lost to defects Bad units priced at the ideal cycle time.
- 14 min
- Fully productive time
- 371 min
OEE multiplies three independent ratios — availability, performance and quality — into a single number between 0 and 100%. Because it is a product, a line that runs perfectly but produces 10% scrap cannot score above 90%, no matter how fast it runs. That is the point of the metric: it refuses to let a strong dimension hide a weak one.
Most OEE arguments at a plant are really arguments about definitions. This calculator uses the planned production time as the denominator, treats changeover and breakdowns as downtime, and charges performance loss against the ideal cycle time you enter. The loss breakdown below the results tells you how many minutes each of the three factors costs you per shift, which is what actually decides where to spend the improvement budget.
How the result is calculated
OEE = Availability × Performance × Quality- Availability = (Planned production time − Downtime) ÷ Planned production time
- Performance = (Ideal cycle time × Total count) ÷ Run time
- Quality = Good units ÷ Total count
- Fully productive time = Planned production time × OEE
Variables
| Symbol | Meaning | Unit |
|---|---|---|
A | Availability | % |
P | Performance | % |
Q | Quality | % |
ICT | Ideal cycle time | sec/unit |
Worked example
A filling line runs a 480-minute shift with 45 minutes of changeover and breakdown. The ideal cycle time is 55 seconds per unit. The line produces 420 units and 405 pass inspection first time.
- Run time = 480 − 45 = 435 min
- Availability = 435 ÷ 480 = 90.6%
- Performance = (55 s × 420) ÷ (435 × 60 s) = 23,100 ÷ 26,100 = 88.5%
- Quality = 405 ÷ 420 = 96.4%
- OEE = 0.906 × 0.885 × 0.964 ≈ 77.3%
OEE 77.3%, with roughly 45 minutes lost to downtime, 50 minutes to speed loss and 14 minutes to defects. Availability is the largest single loss, so the next improvement project should attack changeover time rather than operator speed.
What this calculation does not cover
- Performance is only as honest as the ideal cycle time you enter. Using your best observed run inflates Performance and hides real speed loss — use the OEM rated rate or the theoretical rate from the machine specification.
- Planned downtime (breaks, planned maintenance, no-demand periods) must be excluded from planned production time. If you include it, Availability will look artificially bad.
- A Performance figure above 100% means the ideal cycle time is too slow, or the count includes units produced during a period you also counted as downtime. Both are data-quality problems, not good news.
- OEE does not weight losses by cost. Losing an hour on a $40/hour cell and a $400/hour cell both cost one hour of Availability.
- OEE is not comparable across plants unless the denominators are defined identically. Publish your definition alongside the number.
Frequently asked questions
What is a good OEE score?
85% is the long-standing world-class benchmark popularised by Seiichi Nakajima, built on 90% availability, 95% performance and 99.9% quality. Most discrete manufacturers run between 55% and 70% once measurement is honest. Treat 85% as a direction, not a target to hit next quarter — moving from 60% to 70% is a substantial programme of work.
Should changeover time count as downtime in OEE?
Yes, under the standard definition changeover is an availability loss, because the equipment is not producing saleable output. Some plants track a separate OEE variant that excludes planned changeover to isolate unplanned losses. Either is defensible — what matters is that you pick one, document it, and apply it consistently so trends are comparable over time.
Why is my Performance over 100%?
Almost always one of three causes: the ideal cycle time is set slower than the machine can physically run, the unit count includes parts made before or after the measured window, or some downtime was excluded from the run time. Check the count window first — it is the most common error in manual OEE collection.
Does OEE work for a line rather than a single machine?
Yes, but you must decide between line OEE (treat the whole line as one asset, using the bottleneck cycle time as the ideal) and average machine OEE across the line. Line OEE is the number that matters commercially because it reflects actual output; averaging individual machine OEEs will always look better and will mislead you.