MTBF tells us the most frequent failures within a process. Mean Time means, statistically, the average time. Mean Time Between Failures is two important KPI's in plant maintenance. In other words, the mean time between failures is the time from one failure to another.
Mean Time Between Failures = Total up time / number of breakdowns
= (Total calendar days-Failure days)/ number of breakdowns
= (Total calendar days-Failure days)/ number of breakdowns