Variables
Description
What is this formula?
The Failure Rate measures how frequently failures occur during a specified operating period.
It is one of the most fundamental metrics in reliability engineering and maintenance management.
When to use it
Use this formula when:
- Evaluating equipment performance.
- Comparing reliability of assets.
- Estimating maintenance requirements.
- Monitoring operational reliability.
- Calculating reliability functions and MTBF.
Example
A fleet of pumps accumulates:
T = 50,000 h
During this period:
F = 25 failures
Formula:
λ = F/T
Substitution:
λ = 25/50,000
λ = 0.0005 h⁻¹
Result:
The failure rate is 0.0005 failures per hour.
Applications
- Reliability engineering
- Maintenance planning
- Asset management
- Risk analysis
- Equipment performance monitoring
Note
This calculation provides an average observed failure rate over the analyzed period. In real systems, the failure rate may change over time due to early-life failures, aging, wear, maintenance practices, or operating conditions. Therefore, λ should be interpreted as an average estimate unless a constant-failure-rate model has been validated.