Of the time the machine was supposed to run, how much it actually did.
Availability is the first and most visible factor in overall equipment effectiveness, and the one shops usually start tracking before anything else. The reason is simple: when the machine is not running, everyone can see it. Slow running and quality losses can hide. A stopped machine cannot. Availability puts a number on the obvious problem and creates the starting point for diagnosing why it is happening.
"Availability is the OEE factor you can see from across the shop."
The calculation is simple, but the definitions need to be tight. Planned production time is the window during which the machine was supposed to be producing. It excludes anything the shop deliberately set aside as non production time: meetings, scheduled breaks, full shift shutdowns. It includes planned events that happen during production, like changeovers and preventive maintenance windows, because the convention is that these reduce availability even when they are planned. Run time is the share of planned production time during which the machine was actually running and producing parts. Dividing the second by the first gives availability.
Availability captures two of the six big losses: equipment failure (unplanned breakdowns) and setup or adjustment (changeover time, including any adjustment needed before the first good part). Both reduce run time. The losses can be tracked separately so the team can see whether the bigger drag is unplanned breakdowns or planned changeovers; the response to each is different. Breakdowns come down through preventive maintenance, predictive maintenance, and autonomous maintenance. Changeovers come down through quick changeover work.
Availability is related to but distinct from the reliability metrics. Mean time between failures and mean time to repair combine algebraically to predict availability: availability equals MTBF divided by the sum of MTBF and MTTR. That relationship is useful for diagnosis. If availability is dragging, looking at whether MTBF or MTTR is the bigger drag tells the team where to invest.
Picture a 25 person fab shop with a press brake that is the bottleneck for a third of the work. Availability tracking over two weeks shows 78 percent. Below that, the breakdown: changeover loss 14 percent, breakdown loss 6 percent, waiting on material 2 percent. Each of those buckets is actionable independently. The changeover loss is the biggest target; quick changeover work can probably take it from 14 percent to 7 percent. The breakdown loss points to a single chronic issue with the backgauge that operations had been working around. The waiting on material is a scheduling problem, not an equipment problem.
A focused effort on each bucket over a quarter lifts availability from 78 percent to 88 percent. That ten point gain is roughly 50 minutes of additional run time per shift on the bottleneck, which translates directly to throughput. The shop did not buy a new press brake. It tracked availability honestly, broke down the losses, and attacked them in the right order.
Availability is one of three factors in overall equipment effectiveness, multiplied against performance rate and quality rate. It is the metric that downtime tracking directly feeds. The two equipment reliability metrics that explain availability arithmetically are mean time between failures and mean time to repair.
The questions we hear most about this term.
Long-form guides that pick up where this definition leaves off, written for manufacturers running Arda today.
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