Mean time to repair looks like a maintenance measure and is mostly a logistics measure. The arithmetic is trivial; the decision that matters is what you put inside the clock, because that choice determines whether the number is about how fast a technician works or about how well the whole response is organised.
The formula and what to include
How to calculate mttr: total time spent on repairs divided by the number of repairs. The mttr calculation is unambiguous once you decide when the clock starts. Start it when the technician picks up a spanner and you measure the workshop. Start it when the asset stopped, including detection, notification, travel, diagnosis and waiting for parts, and you measure the response. The second is more uncomfortable and far more useful, because most of the elapsed time in a real failure is not spent turning spanners.
What is mttr in maintenance actually used for
Chiefly as a lever separate from failure frequency. Reducing MTTR is done through spares held for critical assets, documented procedures for rare tasks, access that does not require dismantling something else first, and skills coverage across shifts. None of those reduce how often things fail; all of them reduce what a failure costs. That makes MTTR the more actionable of the two headline numbers in the short term, which is why it belongs in front of a planner rather than only in a report.
The PF curve and where reliability work fits
The pf curve describes the interval between the point a failure becomes detectable and the point the asset actually fails. It is the concept that justifies inspection intervals: if the detectable-to-failure window is six weeks, inspecting every three months will miss it. Reliability and maintenance meet exactly here. Maintenance reliability work, and reliability centered maintenance software that supports it, is largely about finding those windows for the assets that matter and setting inspection frequency inside them, which is a more defensible basis for an interval than any manual provides.
Questions people ask about mttr formula
What is the MTTR formula?
Total repair time divided by the number of repairs. The decision that matters is when the clock starts: at the spanner, or when the asset stopped including detection, travel and waiting for parts.
How do you reduce MTTR?
Spares for critical assets, documented procedures for rare tasks, access that does not require dismantling something else, and skills coverage across shifts. None reduce failure frequency.
What is the PF curve?
The interval between a failure becoming detectable and the asset actually failing. It is what justifies an inspection interval: a six-week window is missed by a quarterly inspection.