Mean Time to Failure
Mean Time to Failure, or MTTF, is the average operating life of non-repairable items before failure.
What this term means in maintenance
Mean Time to Failure, or MTTF, is the average operating life of non-repairable items before failure.
MTTF formula
MTTF = Total operating time accumulated by the component population ÷ Number of failed components
MTTF is generally used for items that are replaced rather than restored after failure.
Practical example
Five identical components accumulate 10,000 operating hours before all five have failed.
MTTF = 10,000 ÷ 5 = 2,000 hours
The result represents the average operating life observed for that population under those conditions.
Difference between MTTF and MTBF
MTBF is normally used for repairable assets that return to service after failure. MTTF describes average life before failure for replaceable or non-repairable items.
How MTTF is used
MTTF can support:
- Replacement planning
- Spare-parts stocking
- Warranty evaluation
- Component comparison
- Lifecycle-cost review
Important limitation
Operating conditions strongly affect component life. Temperature, load, contamination, installation quality, and duty cycle should be considered before comparing MTTF values from different populations.
How this term differs
Mean Time to Failure is average operating life until failure for non-repairable items or populations. It is related to Mean Time Between Failures, Failure Rate, and Failure Frequency, but these terms describe different records, measures, roles, strategies, or decisions and should not be used interchangeably.
Related concepts
Related maintenance terms
Keep exploring connected CMMS, reliability, and maintenance planning terms.
Mean Time Between Failures
Mean Time Between Failures, or MTBF, is the average operating time between failures of a repairable asset during a defined period.
Failure Rate
Failure rate is the number of failures observed per unit of operating time for an asset or defined equipment population.
Preventive Maintenance
Preventive maintenance is planned work performed at defined time, usage, or meter intervals to reduce the likelihood of equipment failure or deterioration.
Glossary FAQs
- What is the MTTF formula?
MTTF equals total accumulated operating time divided by the number of failed non-repairable items.
- What is the difference between MTTF and MTBF?
MTTF is normally used for non-repairable items. MTBF is used for repairable assets that return to service.
- Can MTTF support spare-parts planning?
Yes. It can help estimate replacement demand when component populations and operating conditions are comparable.