What this calculator does
Failure rate expresses how often qualifying failures were observed per operating hour, cycle, or other unit of exposure. It is the reciprocal of MTBF only when both are based on the same repairable population and data scope.
When to use it
Use a rate when you need a probability-model input or want to normalize failures across different operating exposure. It is often more convenient than an interval for a fleet with variable hours.
Inputs and formula
Count only defined failure events and state the exposure clock. λ = failures ÷ total operating time
Worked example and interpretation
12 failures during 6,000 operating hours gives 0.002 failures per hour, equivalent to a reciprocal interval of 500 hours. The rate is a historical estimate, not proof that failures are random.
Practical notes and limitations
Do not feed an observed rate into an exponential reliability model without checking for infant mortality, wear-out, seasonality, common-cause events, and changing duty. Stratify the data when these conditions materially change the failure mechanism.