Definition
Operational availability (可動率) is the proportion of time a machine runs normally when you want it to run. If a process is called on to operate for sixty minutes and it actually runs — producing good parts at the standard rate — for fifty-four of them, stopping for the other six on a jam, a tool-change overrun, or a minor breakdown, its operational availability is 90%. The target is always 100%: whenever the schedule calls for the equipment, it should work.
This is one of two equipment metrics that sound alike in Japanese and are constantly confused. Operational availability is the one Toyota manages on the shop floor, because it isolates a single question — is the equipment reliable when needed? — from the entirely separate question of how much the equipment is needed at all.
Japanese Origin
The two metrics are a deliberate pair, and the distinction is encoded in the kanji, much as it is with jidoka.
- 稼働率 (kadōritsu) — the utilization rate (or operating rate). 稼 means “to operate for gain / to earn,” paired with 働, the “work” character that carries the person radical (亻). It measures how much of the available capacity is actually used to produce.
- 可動率 — the operational availability. 可 means “able / possible,” paired with 動 (“to move”). Literally the “able-to-move rate” — the fraction of the time the equipment can run normally when called upon.
Here is the trap: 可動率 would normally also be read kadōritsu — identical in speech to 稼働率. Because the two are completely different management indicators, Toyota deliberately reads 可動率 as べきどうりつ (bekidōritsu) to keep them apart in conversation. This is the same device Toyota uses with jidoka, writing 自働化 with the person radical to set it apart from ordinary automation, 自動化. In English the pair is usually rendered utilization rate (稼働率) and operational availability (可動率).
Why Toyota Manages Availability, Not Utilization
The two metrics behave in opposite ways, and conflating them leads directly to waste.
- Utilization rate (稼働率) rises and falls with customer demand. If a machine could make 2,000 units in a shift but the customer needs only 1,000, utilization is 50% — and that is correct. If demand spikes and the line runs overtime, utilization can even exceed 100%. Because it tracks demand, utilization is a management and investment number — are we sizing and loading our assets sensibly? — not something the floor should try to maximize.
- Operational availability (可動率) is unaffected by demand. It asks only whether the equipment ran when it was supposed to. Its ceiling is 100%, and 100% is the legitimate target, so it cleanly reflects the results of maintenance, quick changeover, and fast abnormality response — the things the floor actually controls.
The danger of confusing them is concrete. If the floor is told to “raise utilization,” the way to do that is to make more parts — whether or not anyone needs them. That is overproduction, the worst of the seven wastes: capital and material converted into unsold inventory that then hides other problems. Taiichi Ohno’s point was that the goal of a machine is not to “be able to run” every minute but to make money — to run well when needed. Chasing a high utilization number works directly against just-in-time. Managing availability does not: a machine that reliably runs when called upon, and sits quietly when it is not, is exactly what a leveled, pull-based system requires.
Calculation
Operational availability is commonly calculated as:
可動率 = (good units produced × standard cycle time) ÷ time the equipment was required to run
The numerator is the output the equipment should have produced in the time available; the denominator is the time it was actually called on to run. Downtime from breakdowns, changeover overruns beyond standard, and minor stoppages all pull the figure below 100%. This is the equipment-reliability portion of what OEE captures as availability (see the TPM entry).
Common Misunderstandings
Treating a high utilization rate as good. A utilization rate near 100% is often celebrated as “the equipment is working hard.” But unless demand genuinely requires that output, a high utilization rate means overproduction. Demand sets utilization; the floor should not try to drive it up.
Trying to improve availability by running faster. Availability is about running normally when needed — not above the standard rate. Pushing equipment past its design speed to recover lost time degrades quality and accelerates wear, and because the standard cycle time is fixed in the formula, it does not even raise the number honestly.
Confusing the two because they sound identical. Both are kadōritsu in ordinary reading. If a report — or a supplier — says “kadōritsu,” confirm which kanji is meant, 稼働率 (utilization) or 可動率 (availability), before acting on it. They point in different directions.
Aiming for 100% utilization. 100% availability is the right target; 100% utilization usually is not. An asset deliberately sized with capacity to spare — so it can keep up during demand peaks without overtime — will, and should, show utilization well below 100%.