Failure Rate
Failure rate is the number of failures observed per unit of operating time for an asset or defined equipment population.
What this term means in maintenance
Failure rate is the number of failures observed per unit of operating time for an asset or defined equipment population.
Failure-rate formula
Failure rate = Number of failures ÷ Total operating time
The result may be expressed as failures per hour, day, cycle, kilometre, or another relevant operating unit.
Practical example
A group of assets experiences six failures during 3,000 operating hours.
Failure rate = 6 ÷ 3,000 = 0.002 failures per hour
This can also be expressed as approximately one failure every 500 operating hours for the observed period.
Relationship to MTBF
Under appropriate assumptions:
Failure rate ≈ 1 ÷ MTBF
This inverse relationship is useful for simple comparisons, but it should not be applied blindly when failure behavior changes with age or operating conditions.
How failure rate is used
Failure rate can help teams:
- Compare asset populations
- Track reliability trends
- Estimate expected failure demand
- Review component performance
- Measure the effect of corrective actions
Common mistake
Do not mix operating time and calendar time, combine unrelated failure definitions, or compare equipment populations operating under very different loads and environments without context.
How this term differs
Failure Rate is failures divided by operating exposure. It is related to Mean Time Between Failures, Failure Frequency, and Mean Time to Failure, 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.
Mean Time to Failure
Mean Time to Failure, or MTTF, is the average operating life of non-repairable items before failure.
Root Cause Analysis
Root cause analysis is a structured investigation used to identify the underlying conditions that allowed a failure or problem to occur and determine actions that reduce recurrence.
Glossary FAQs
- What is the failure-rate formula?
Failure rate equals the number of failures divided by total operating time for the same period and equipment population.
- How is failure rate related to MTBF?
Under appropriate assumptions, failure rate is approximately the inverse of MTBF.
- Can failure rate be zero?
Yes. A period with no recorded failures has a calculated failure rate of zero, but it may be too short to support a meaningful reliability conclusion.