MTBF stands for Mean Time Between Failures. What does it measure?

• A. Minimum Time Between Failures; minimum uptime.
• B. Mean Time Between Failures; reliability metric indicating average time between failures.
• C. Maximum Time Before Failure; time until failure threshold.
• D. Time between manufacturing defects.

Answer: (B)

MTBF measures how long, on average, a repairable system will operate before a failure occurs. It’s the expected time between failures during normal use. You find it by dividing the total time the equipment was running (uptime) by the number of failures that occurred in that period. For example, if a machine runs 10,000 hours and has 50 failures, the MTBF is 200 hours. A higher MTBF means the system tends to run longer between failures, indicating better reliability. This isn’t about how long the system stays up in a single cycle, nor about repair time or manufacturing defects; it specifically tracks the time between failure events during operation. In many cases with a constant failure rate, MTBF is the reciprocal of that failure rate.