Glossary comparison
FIT vs MTBF: what is the difference?
The difference
MTBF is the reciprocal of a constant failure rate, so it carries the same information as FIT. An MTBF of a billion hours does not mean any part will last that long.
FIT counts failures per billion device-hours. It is the reciprocal view of the same constant failure rate, scaled for very reliable components.
The two terms
FIT
The standard failure rate unit, one failure per billion device hours of operation. Rates from accelerated tests are converted to FIT at a stated use temperature, voltage and confidence level, and FIT values add across components in a system.
MTBF
The average operating time between successive failures of a repairable system. For a constant failure rate it is simply the reciprocal of that rate, so a large MTBF describes a population average and not the expected life of one unit.
Side by side
| Field | FIT | MTBF |
|---|---|---|
| Stands for | Failures In Time | Mean Time Between Failures |
| Type | Acronym | Acronym |
| Domain | Reliability & Quality | Reliability & Quality |
| Group | Reliability modelling | Reliability modelling |