Maintenance and reliability
What is MTTR (mean time to repair)?
MTTR is the average time to restore a failed machine to service. Formula, worked example, how MTTR and MTBF give availability, and a free MTTR calculator.
Quick answer
MTTR (mean time to repair) is the average time it takes to restore a failed machine to working order. It equals total repair time divided by the number of repairs. Lower MTTR means faster recovery. Combined with MTBF it gives inherent availability: MTBF divided by MTBF plus MTTR.
Updated 30 October 2026. Written by the Ajinkya Technologies engineering team, reviewed by Amey Kadle.
Formula
MTTR = total repair time ÷ number of repairs. Availability = MTBF ÷ (MTBF + MTTR)
Worked example: Four breakdowns took 10 hours in total to fix. MTTR = 10 ÷ 4 = 2.5 hours. With an MTBF of 180 hours, inherent availability = 180 ÷ 182.5 = 98.6%.
MTTR and availability calculator
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- MTTR
- 2.5 hours
- Inherent availability
- 98.6%
MTTR (mean time to repair) explained
Definitions of MTTR vary, so state which one you use. In maintenance it usually runs from the moment the machine stops until it is back in production, which includes noticing the stop, getting a technician there, diagnosing the fault, finding spares, repairing and testing. Some teams measure only the hands on repair time. The full version is more useful because the waiting parts are often the biggest and the easiest to cut.
Breaking MTTR into its stages shows where time goes. Response time improves with automatic alerts to the right technician. Diagnosis improves with fault history, sensor data and clear troubleshooting guides. Spares delays fall when critical parts are reserved against the asset. Repair and test time falls with standard work instructions and video SOPs at the machine.
MTTR and MTBF together define inherent availability, the share of time a machine can run when only failures and repairs are counted. Improving either one raises availability; for most plants, cutting the waiting inside MTTR is the faster win, while raising MTBF takes longer reliability work.
Key concepts
- Define where MTTR starts and stops
- Response, diagnosis, spares, repair, test
- Automatic alerts cut response time
- Video SOPs and fault history cut diagnosis
- Availability = MTBF ÷ (MTBF + MTTR)
Questions
Does MTTR include waiting for spare parts?
In the full definition, yes: it runs from the stop until the machine is back in service. Some teams report hands on repair time separately to see how much is waiting.
How can we reduce MTTR quickly?
Send stop alerts automatically to the right technician, keep critical spares reserved per asset, and put fault history and video work instructions at the machine through a QR code or tablet.
What is the difference between MTTR and downtime?
Downtime is the total time lost. MTTR is the average per repair, so downtime from failures is roughly the number of failures multiplied by MTTR.
References
How we help with MTTR
Our maintenance systems put QR codes on assets that open the history and video SOP on a phone, and send stop alerts to the right technician, which shortens the waiting inside MTTR.
Interactive 3D demo with simulated data: vibration rises, the alert fires, you decide.
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