MTBF Calculator

Mean Time Between Failures (MTBF) = total_operational_time / number_of_failures. For example, if a fleet of 100 servers accumulates 876,000 operating hours and experiences 15 failures, MTBF = 876,000 / 15 = 58,400 hours per failure. MTBF applies to repairable systems. For non-repairable items (like a capacitor), use MTTF (Mean Time To Failure).

Collect total operational time across all units in the field (unit_hours = sum of each unit's operating hours since last repair or installation). Count the total number of failures across all units in that period. MTBF = total_unit_hours / total_failures. A 90% confidence interval for the true MTBF requires chi-squared distribution tables; the observed MTBF is a point estimate.

MTBF (Mean Time Between Failures) is used for repairable systems and includes the repair time in the cycle. MTBF = MTTF + MTTR. MTTF (Mean Time To Failure) is the expected time until the first failure for non-repairable items. For practical uptime calculations with short repair times relative to MTBF, MTBF is approximately equal to MTTF.

Manufacturer MTBF figures are typically derived from MIL-HDBK-217 or Telcordia SR-332 reliability prediction models at standard operating conditions, not from field failure data. Field MTBF often differs from predicted values due to actual operating conditions (temperature, humidity, vibration), workload intensity, and quality of maintenance. Treat manufacturer MTBF as a relative comparison tool, not an absolute prediction.

Availability = MTBF / (MTBF + MTTR). With an MTBF of 10,000 hours and MTTR of 4 hours, availability = 10,000 / 10,004 = 99.96%. To achieve higher availability, either increase MTBF (better components, better design, better maintenance) or decrease MTTR (better monitoring for faster fault detection, spare parts availability, trained technicians, automation).