What this calculator does
The expected count is E[N] = population × failure rate × exposure time. It converts a rate into a planning mean, not a promise of the exact number of work orders.
When to use it
Use it for first-pass staffing, repair-kit, warranty, or field-service forecasts when a constant-rate approximation is justified.
Inputs and formula
Failure rate must be per item-hour and exposure must be in hours. Population can represent identical operating assets or a forecasted cohort.
Worked example and interpretation
One hundred items at 0.0002 failures per item-hour over 500 hours yield 10 expected failures. A real period could contain fewer or more due to random variation.
Practical notes and limitations
Do not use a single fleet average when failure intensity changes sharply with age or duty. For age-dependent behavior, fit a distribution and use Weibull reliability.