MTBF Calculator
Work out mean time between failures for one asset from its scheduled hours, unplanned downtime, and failures.
Example only. The starting values are invented: a pump scheduled to run 16 hours a day for 250 days.
Mean time between failures
792 hours
The average operating hours between breakdowns.
MTBF (mean time between failures) is the average operating time an asset gets between breakdowns. A higher figure means the asset fails less often.
Formula
MTBF = T ÷ F
- T is operating time: scheduled hours less unplanned downtime hours.
- F is the number of failures in the same period.
A failure is a breakdown: the asset stops being able to do its job. Planned stops, such as preventive maintenance, are not failures and are not part of T.
The figure assumes a steady failure rate across the period. That holds in the middle of an asset’s life, not at its start or its end. Mean time to failure, MTTF, is the measure for parts that are replaced rather than repaired.
The MTBF and MTTR guide works through the method with a pump. Maintenance metrics and KPIs covers the other figures to track beside MTBF.
FixAhead reports MTBF per asset. See the reporting features.
Source
NIST and SEMATECH, e-Handbook of Statistical Methods, section 8.4.5.1: MTBF is total operating time divided by the total number of failures. U.S. Army, TM 5-698-1, glossary: MTBF is the exposure time divided by the number of failures in that period. U.S. Department of Defense, MIL-HDBK-338B: MTBF is a basic measure of reliability for repairable items.
Worked example
Example only. The starting values are invented: a pump scheduled to run 16 hours a day for 250 days.
- Scheduled hours: 4,000
- Unplanned downtime hours: 40
- Failures: 5
T = 4,000 − 40 = 3,960 hours MTBF = 3,960 ÷ 5 = 792 hours
Over the period, the pump ran an average of 792 hours between breakdowns.