Sit a maintenance manager and a production manager in the same meeting and you will eventually hear it: "But the machine had 95% uptime last month." "Then why is OEE availability only 78%?" Both are right, because they are measuring different things. Confusing availability with uptime is one of the most common sources of mistrust in manufacturing metrics, and clearing it up makes both numbers more useful.
Uptime and OEE availability answer different questions — both can be true at once.
Uptime is a reliability measure: the proportion of time an asset was operational and available, as opposed to broken down. It is often calculated over total or calendar time and is closely related to reliability metrics like MTBF. It answers: "How much of the time was this machine capable of running?"
OEE availability is stricter and more specific. It is run time divided by planned production time, the time you actually intended to be producing. Crucially, it counts both breakdowns and planned setups/changeovers as availability losses, and it is measured only against scheduled production time, not all calendar time. It answers: "Of the time we planned to produce, how much were we actually running?"
Changeovers. A machine in setup is not broken, so it counts as uptime, but it is not running, so OEE availability drops. This alone explains many gaps.
Different denominators. Uptime is often over total time; OEE availability is over planned production time. Same machine, different base, different percentage.
Minor stops. Depending on definitions, short stoppages may be treated differently in each metric.
So a machine can have excellent uptime and mediocre OEE availability at the same time, and nobody is wrong.
Use uptime and reliability metrics like MTBF and MTTR to judge asset health and maintenance effectiveness. Use OEE availability to judge how well planned production time is being converted into running time, including the changeover losses uptime ignores. They are complementary lenses, not rivals; problems start only when people assume they are the same number. For the bigger picture of how time is classified, see the OEE time model.
Most disputes are really definition disputes: what counts as planned time, as a changeover, as a minor stop. Without agreed definitions and automatic capture, each team computes its own version and the meeting goes in circles, with the underlying detail lost as dark data.
Fabrico captures machine states automatically and classifies time consistently, so availability, uptime and the losses between them all come from one trusted source. Maintenance and production see the same data, defined the same way, and can finally discuss how to improve it instead of arguing about whose number is correct.
No. Uptime measures how much of the time a machine was operational, often over total time. OEE availability is run time over planned production time and counts changeovers as losses.
Mainly because OEE availability counts changeovers and setups as losses and is measured against planned production time, while uptime usually does not and is measured over total time.
Both. Use uptime/MTBF for asset reliability and OEE availability for how well planned production time is used. Just keep their definitions distinct.
One source of truth for availability and uptime. See how Fabrico classifies machine time consistently so maintenance and production stop arguing about numbers. Book a demo today.
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