Mean Time To Repair (MTTR) and Mean Time Between Failure (MTBF) are the two most important key performance indicators or metrics that are used in the Maintenance process or reliability engineering to measure the performance of machines and equipment. MTTR and MTBF KPIs tools are widely used by the Lean Manufacturing industries and IATF 16949-certified Automotive industries to enhance Overall Equipment Effectiveness.
Mean Time To Repair and Mean Time Between KPIs are very useful Lean Tools of manufacturing industries.
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MTBF | MEAN TIME BETWEEN FAILURE
It is the average time between two failures of the same system or component. It is calculated by dividing the system’s overall uptime or Available Operational time by the number of failures.
- The MTBF KPI monitors the availability and reliability of an equipment/machine.
- The system is more reliable if the time between failures is higher.
- The goal for most organizations is to maintain the mean time between failure (MTBF) higher as much as possible.
- This metric is used for failures in repairable systems.
MTBF Formula | MTBF Calculation
Formula MTBF = Operational Time / No. of breakdowns or failure.
[Operational Time = Available Time – Breakdowns or Downtime hours]
Mean Time Between Failure is calculated using an arithmetic mean. The data you can choose from any period (one week, one month,  six months, one year, or more ) and divide that period’s available operational time by the number of breakdowns or failures that occurred in a particular period.
Let’s calculate the available hours of one machine in one month.
Machine Available Time  = 3*8*25= 600 hours [3 shifts of 8 hours X no. of working days in a month]
No. of breakdowns occurred in a month = 2 Nos. [ 2hrs and 3 hrs each ]
Total Breakdown hours = 5 hours
Actual Operational time = 600-5 = 95 hours
MTBF = 600-5/2 = 297.5 hours
MTTR | MEAN TIME TO REPAIR
It is the average time to repair a machine or equipment after failure/breakdown. It is calculated by dividing the total repair time or total breakdown time of the machine or system by the number of repairs or the number of breakdowns. MTTR is also called the Mean Time To Recovery.
MTTR Formula | MTTR Calculation
Formula MTTR = Breakdowns or Repairs or Downtime hours of machine or system /Â No. of breakdowns or failures or RepairsÂ
Let’s Say,
No. of breakdowns occurred in a month = 2 Nos. [ 2hrs and  3 hrs each ]
Therefore, total breakdown hours = 5 hours
MTTR = 5/2 = 2 hours
