The OEE formula
- Availability = run time ÷ planned production time. Run time is planned time minus unplanned downtime.
- Performance = (ideal cycle time × total count) ÷ run time. How close to full speed the machine ran while it was running.
- Quality = good count ÷ total count.
Multiplied out, OEE simplifies to good count × ideal cycle time ÷ planned production time — the share of planned time spent making good parts at full speed. That's why this calculator can convert every loss into minutes.
What's a good OEE?
The figure you'll hear is 85% as world-class, a benchmark that traces back to the early TPM literature. You’ll also see “around 60%” quoted as typical for discrete manufacturing, but there’s no rigorous industry-wide study behind that figure. Treat both numbers as rough — OEE depends heavily on how you define planned time and ideal cycle time, so comparing plants is shaky. Comparing a line against its own history is reliable.
Common OEE mistakes
- Using a "standard" rate instead of the true ideal. If the cycle time you enter is slower than what the machine can actually do, performance looks better than it is. A performance above 100% is the giveaway.
- Hiding downtime as planned. Calling changeovers or waiting-for-material "planned" raises availability on paper and hides the biggest improvement opportunity.
- Counting rework as good. A part that needed a second pass cost time twice. Quality should count first-pass good only.
- Chasing the OEE number instead of the losses. Two lines at 65% can have completely different problems. The loss breakdown matters more than the headline.
The six big losses
TPM groups OEE losses into six categories, two under each factor. Availability: equipment failures, and setups or adjustments. Performance: idling and minor stops, and reduced speed. Quality: process defects, and startup rejects. Tracking downtime against these categories tells you whether you have a maintenance problem, a changeover problem, or a process problem.
FAQ
Is planned maintenance part of OEE?
Usually no — planned PM time is subtracted before planned production time, so it doesn't count against availability. If you want a number that does penalize all downtime, look at TEEP (total effective equipment performance), which uses all calendar time.
What if I only know the ideal rate, not the cycle time?
Convert it: ideal cycle time in seconds = 3,600 ÷ ideal units per hour. 3,600 parts per hour is a 1-second cycle.
Why is my performance over 100%?
The ideal cycle time is set too slow — the machine ran faster than what you told the calculator was its maximum. Use the true design or demonstrated best speed.
Is my data uploaded anywhere?
No. The calculation runs in your browser.
Sources & standards
- Nakajima, Seiichi. Introduction to TPM: Total Productive Maintenance. Productivity Press, 1988. — Origin of OEE, the six big losses, and the 85% world-class benchmark.
The formulas and six big losses follow Nakajima’s TPM definitions. Benchmarks are rough guides; compare a line against its own history first.