Key takeaways
Short answer: Uptime and availability both answer "was the machine up," but they measure against different clocks. Uptime counts powered-on time. Availability counts productive time against the time you planned to produce. A line can be powered on all shift (high uptime) yet lose hours to changeovers and minor stops (low availability).
Availability is the number that ties to lost production, which is why it sits inside OEE and uptime does not.
Uptime is the proportion of time an asset is on and capable of running. It is the metric IT and facilities teams use for equipment that should essentially never be off, like servers or compressors.
It answers a binary question: is the asset up or down? That simplicity is its strength and its weakness. Uptime tells you the machine was powered and ready. It does not tell you whether it was actually making good product during that time.
Most uptime definitions also fail to separate planned stops from unplanned ones. An asset idle during a scheduled changeover can still count as "up," which is exactly where uptime and availability start to diverge.
Availability is run time divided by planned production time. It is the first of the three factors in OEE, alongside performance and quality.
The key word is planned. Availability only counts the time you intended to be producing, then asks what fraction of that time the asset was actually running. Planned downtime (scheduled maintenance, planned changeovers, no orders) is excluded from the clock. Unplanned downtime (breakdowns, unplanned changeovers, material starvation) is what drags the number down.
That makes availability a direct measure of lost production opportunity, not just power state. A working preventive maintenance schedule is one of the main levers that moves it.
The cleanest way to see the difference is the denominator each one uses:
This is why the two numbers can disagree sharply. A machine that is on 24/7 but only scheduled to run one shift can show very high uptime and mediocre availability, because the availability clock only covers the scheduled shift and counts every unplanned stop inside it.
Take a line scheduled to produce for 8 hours (480 minutes). During the shift it is powered on the whole time, but it loses 60 minutes to an unplanned breakdown and 30 minutes to an unplanned changeover overrun.
Same shift, same machine, two very different stories. The uptime number hides the 90 minutes of lost production that availability exposes.
Availability is the first factor in OEE: OEE equals availability times performance times quality. Uptime does not appear in the formula at all, which is the clearest signal of which metric production teams should lead with.
Because availability is multiplicative in OEE, a few points lost here flow straight through to the headline number. Recovering unplanned downtime, usually through faster response and better work order management, is often the highest-leverage move on the whole OEE figure.
The hard part is not defining availability. It is capturing every unplanned stop accurately and tying it to the asset and work order behind it, so the number reflects reality instead of what operators had time to log.
Fabrico measures availability from the live machine signal, separates planned from unplanned downtime automatically, and links each stop to the maintenance response. To see your real availability against your planned schedule, book a demo.
No. Uptime is powered-on time against total time. Availability is run time against planned production time. Availability is stricter and is the version that feeds OEE.
Yes, and it is common. An asset powered on through every shift can still lose large chunks of scheduled production to unplanned stops, which only availability captures.
Availability, for production equipment. It maps directly to lost production and to OEE. Reserve uptime for always-on support assets where the only question is whether the asset is on.
No, if it is classified correctly. Planned downtime is excluded from the availability clock, so scheduled maintenance does not penalize the number. Misclassifying it as unplanned is what causes confusion.
It is the first of the three OEE factors. Because OEE multiplies availability by performance and quality, every point of availability lost reduces the OEE result directly.
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