Glossary

Mean time between failures (MTBF)

The average time a repairable system operates between one failure and the next, used to measure reliability.

Also called: MTBF

Mean time between failures is a reliability metric for equipment that gets repaired and returned to service, expressing, on average, how long it runs before something breaks down. It applies to repairable systems specifically; the related but distinct concept for non-repairable components that are simply replaced is mean time to failure.

The formula is total operating time / number of failures over the period measured. A higher MTBF means more reliable equipment, but the figure is an average across possibly very different failure events, so it says nothing about the pattern of failures, whether they cluster early, occur randomly, or increase with age, which matters for planning maintenance. It is closely related to mean time to repair, the average time to fix a failure once it occurs, and the two together determine equipment availability.

MTBF is a standard input to predictive maintenance programs and reliability-centered maintenance planning, and it factors into overall equipment effectiveness by driving the availability component of that metric. Manufacturers use it to set maintenance intervals, plan spare-parts inventory, and compare equipment models or vendors. A common pitfall is treating MTBF as a guarantee for any individual unit, or as a distribution-free number: two machines with identical MTBF can have very different failure patterns, sometimes visible in first-pass yield trends leading up to a breakdown, and very different risk profiles as a result.

Last reviewed September 22, 2026

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Related terms

Predictive maintenance Using sensor data and models to predict when equipment is likely to fail so it can be serviced before it breaks down. Overall equipment effectiveness (OEE) A composite manufacturing metric combining availability, performance, and quality into one score of how well equipment is used. First-pass yield (FPY) The percentage of units that come out of a process correctly on the first attempt, with no rework or scrap. Digital twin A live virtual model of a physical asset or process, kept synchronized with real sensor data, used to simulate and predict behavior.

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