TeamAssurance

    What is MTBF?

    Short answer

    MTBF, mean time between failures, is the average operating time between breakdowns of a repairable asset, calculated as total operating time divided by the number of failures in that period. A rising MTBF means the asset is failing less often. It is usually tracked with MTTR, mean time to repair, which shows how quickly failures are fixed; together they describe availability.

    Last updated · TeamAssurance

    The MTBF formula

    MTBF = total operating time ÷ number of failures

    A packing machine that ran for 600 hours in a month and broke down four times has an MTBF of 150 hours. Operating time excludes planned downtime; only time the machine was expected to run counts.

    MTTR and availability

    • MTTR (mean time to repair) = total repair time ÷ number of failures. If the four breakdowns took eight hours in total, MTTR is two hours.
    • Availability ≈ MTBF ÷ (MTBF + MTTR) = 150 ÷ 152 = 98.7%.

    Raising MTBF (fewer failures) and lowering MTTR (faster recovery) both raise availability, the first factor in OEE.

    What MTBF is good for

    • Comparing an asset with its own history: is reliability improving after a change?
    • Ranking assets by reliability to focus maintenance effort.
    • Testing whether a preventive or condition-based programme is working.

    What it is not good for

    • Comparing different kinds of equipment.
    • Predicting an individual failure; it is an average.
    • Assets with very few failures, where one event swings the figure.

    Improving MTBF

    1. Record every failure against the asset with a cause code.
    2. Find the few causes behind most failures (they cluster).
    3. Remove them through root cause analysis and planned, preventive or condition-based maintenance.
    4. Watch MTBF over months; a real improvement shows as a sustained rise.

    MTBF on a tier board

    Track MTBF and MTTR for critical assets on the Tier 2 or Tier 3 board with the top failure causes beside them. A falling MTBF is a signal for structured problem solving, not a target to explain away.

    How TeamAssurance helps

    TeamAssurance records breakdowns and small stops against each asset with cause codes, so MTBF and MTTR can be measured per asset and the causes behind them ranked. Recurring causes move into structured problem solving, and preventive and condition-based work is scheduled and tracked in the asset management capability.

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    Frequently asked questions

    What is a good MTBF?

    There is no universal figure; it depends on the asset and its duty. The useful comparison is an asset's MTBF against its own history and against the target set when the maintenance strategy was chosen.

    What is the difference between MTBF and MTTF?

    MTBF applies to repairable assets and measures time between failures. MTTF, mean time to failure, applies to non-repairable items such as light bulbs or sealed bearings and measures the expected life before they are replaced.

    How does MTBF relate to OEE?

    Breakdowns reduce availability, the first factor in OEE. A rising MTBF means fewer breakdown losses; combined with a lower MTTR it raises availability directly.

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