← Equipment management glossary
Also called: MTBF, mean time between failure.
The report said two thousand hours between failures. The operators said it played up most weeks. Both were true — the small faults were worked around and never logged.
Consistency in what gets recorded matters more than precision in the calculation.
Mean time between failures
MTBF = Total operating time ÷ Number of failures
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Total operating time
Hours the equipment was actually running, not hours it existed.
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Number of failures
Whatever you have decided counts as one. That definition sets the answer, and it is the part nobody writes down.
MTBF, MTTR and MTTF
MTBF — mean time between failures — measures reliability for equipment that gets repaired and put back into service. MTTR — mean time to repair — measures how quickly it comes back, which is maintainability rather than reliability. MTTF — mean time to failure — applies to things that are replaced rather than repaired, like bulbs and bearings.
The pair worth watching together is MTBF and MTTR: reliability and recovery. Equipment that fails rarely but takes a week to fix can be more disruptive than equipment that fails often and is back in an hour.
Three ways it misleads
It is an average, and failures are not evenly distributed. Equipment characteristically fails early (manufacturing defects) and late (wear-out), with a reliable middle. An MTBF of 2,000 hours does not promise 2,000 good hours.
Small samples produce meaningless numbers. MTBF from three failures is arithmetic, not statistics. It is most useful across a fleet of similar items or a long history of one item.
The definition of "failure" decides the answer. If minor faults that get worked around are not logged, MTBF looks excellent while the equipment is visibly unreliable to everyone who uses it. Consistency in what gets recorded matters more than precision in the calculation.
What goes wrong without it
Without failure records tied to specific items, chronically unreliable equipment is defended anecdotally and replaced late, long after its repair spend passed the cost of a new one.
How Itefy handles it
Itefy logs issues and repairs against the individual item, so failure frequency and repair cost per item accumulate as a record rather than as impressions. Read more.