What is MTTF?
MTTF stands for Mean Time To Failure and indicates the average time before a non-repairable component fails.
MTTF is used to predict the lifespan of components that are not repaired but replaced when they fail — such as Sensors, lamps or fuses.
🧮 How is MTTF calculated?
Formula:
MTTF = Total operating time / Number of failed components
For example: If 10 sensors each ran for 10,000 hours before failing: → MTTF = (10 × 10,000) / 10 = 10,000 hours
🔍 MTTF vs. MTBF vs. MTTR
| Term | Description |
|---|---|
| MTTF | For non-repairable components (single use) |
| MTBF | For repairable systems or components |
| MTTR | How long it takes to repair a fault |
MTTF says nothing about repair, only about lifespan before failure.
🏭 Typical applications
- Sensors, relays, lamps, batteries
- Embedded electronics that cannot be serviced
- Backup valves or fail-safe actuators
- Spare-parts inventory analysis
- Lifespan prediction during design (Design for Reliability)
📏 Important in:
- RAMSHEEP analyses
- FMEA and LOPA
- Asset Management and maintenance planning
- Functional Safety (e.g. for one-shot activated systems)
📌 In summary
MTTF is the average time until a non-repairable component fails. It helps with estimating lifespan, risks and inventory management of critical components.