MTTR measures how long, on average, an asset stays down once it fails. It is the second of the two foundational reliability metrics, alongside MTBF.
The formula:
MTTR = total downtime caused by failures / number of failures
If a piece of equipment failed 4 times and the total downtime across those failures was 16 hours, the MTTR is 4 hours. Lower is better.
What MTTR actually measures
MTTR is the elapsed wall-clock time from the moment the asset stops working to the moment it is back in service. It includes:
- Time to detect and report the failure.
- Time to dispatch a technician.
- Time to diagnose the problem.
- Time to source the right part.
- Time to perform the repair.
- Time to test and return to service.
Most of the variance in MTTR comes from the steps before the actual repair: detection, dispatch, diagnosis, and parts. A fast repair is rarely the bottleneck.
How to lower MTTR
- Better detection: sensors and operator reporting that catch failures early.
- Standby parts: keep critical spares on hand so technicians do not wait on procurement.
- Procedures: documented step-by-step repair instructions cut diagnosis and execution time.
- Skills: technicians trained on the most common failures of your specific equipment.
MTTR vs MTBF together
MTBF tells you how often things fail; MTTR tells you how long they stay broken. Multiplied together they describe the availability of an asset. A high-availability operation aims for high MTBF (failures are rare) and low MTTR (when they happen, the asset is back fast).