MTBF

MTBF stands for mean time between failures. It is a reliability metric that estimates the average time a repairable system operates in service before a failure occurs.

It is calculated from field data by dividing the total operational time by the number of observed failures. For a device that runs T hours and experiences N failures, MTBF = T / N. The metric focuses on uptime between faults rather than repair time.

MTBF is related to but distinct from MTTR, the mean time to repair. Availability can be approximated as MTBF / (MTBF + MTTR). In practice, MTBF is used to plan maintenance, predict spare parts needs, and assess reliability trends across devices or systems.

MTBF is highly sensitive to the underlying failure distribution and data quality. It assumes a stationary process with a relatively constant failure rate, which is not valid for wear-out or infant mortality phases. It is an average and does not guarantee timing for any single unit. It does not predict the exact time of the next failure for an individual item.

In reliability engineering, MTBF is commonly complemented by other metrics such as MTTF, MTTR, and life data analysis using distributions like the exponential or Weibull. It should be interpreted with consideration of data size, observation window, and operating conditions to avoid misleading conclusions.