Core Reliability
MTBF Calculator
Mean time between failures from operating time and failure count, or from a known failure rate — with failure rate and mission reliability alongside.
MTBF = T ÷ nResult
- Failure rate λ
- —
- Reliability R(t)
- —
MTBF = operating time ÷ failures
What is MTBF?
Mean Time Between Failures (MTBF) is a fundamental reliability engineering metric that measures the predicted elapsed time between inherent failures of a mechanical or electronic system during normal operation.
MTBF represents system reliability and helps predict:
- Expected number of failures over an operating period
- Corrective-maintenance workload
- Spare parts inventory planning
- System availability forecasting
- Total cost of ownership
MTBF formula
MTBF = Total Operating Time ÷ Number of FailuresMTBF = (Number of Units × Operating Hours per Unit) ÷ Total FailuresHigher MTBF values indicate more reliable systems with longer expected operational periods between failures.
MTBF calculation example
A company operates 10 delivery trucks for one year and tracks all mechanical failures:
| Operating data | Value |
|---|---|
| Number of trucks | 10 |
| Operating hours per truck | 8 h/day |
| Operating days per year | 250 |
| Total failures in year | 25 |
10 × 8 × 250 = 20,000 hours20,000 ÷ 25 = 800 hoursThis means on average, each truck operates 800 hours between failures.
MTBF industry benchmarks
Typical ranges; treat them as orientation, not targets — duty cycle and failure definitions vary.
| Manufacturing equipment | MTBF |
|---|---|
| World class | > 5,000 h |
| Good | 2,000–5,000 h |
| Average | 500–2,000 h |
| Poor | < 500 h |
| Electronic systems | MTBF |
|---|---|
| Server hardware | 50,000–100,000 h |
| Industrial controllers | 100,000+ h |
| Consumer electronics | 10,000–50,000 h |
| Power supplies | 30,000–80,000 h |
| Automotive components | MTBF |
|---|---|
| Engine systems | 3,000–8,000 h |
| Transmission | 5,000–10,000 h |
| Electrical systems | 20,000+ h |
| Suspension | 4,000–12,000 h |
MTBF vs other reliability metrics
MTBF (time between failures) measures reliability — how long a system runs before failing. MTTR (time to repair) measures maintainability — how long repairs take.
Where MTBF is used:
- Maintenance planning: estimate how many breakdowns to staff and stock for (time-based PM intervals need wear-out data such as a Weibull fit, not MTBF)
- Warranty planning: set appropriate warranty periods
- System design: compare component reliability options
- Cost analysis: calculate total cost of ownership
How to use this MTBF calculator
- Single system: enter total operating time and failure count
- From a known rate: switch to “From failure rate” and enter λ
- Time units: choose hours, days, or years
- Mission time: add one to get the probability of running that long without failure
Best practices:
- Use sufficient data for statistical significance
- Track only unplanned failures, not maintenance
- Consider system boundaries and what constitutes failure
- Update MTBF calculations regularly as data accumulates