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Mean Time Between Failure (MTBF) is the average of the run times of a machine, between two failures, for a particular time period. Time period can be one week, one month, one year etc…
How to Calculate Mean Time Between Failure (MTBF)
MTBF is calculated by following formula,
Run time is the total running time of the machine for a particular time period.
Running time can be calculated by reducing total breakdown time from the available time, for a particular time period. Don’t forget to reduce other breaks such as tea break, lunch break, idle time, etc. We only need the time the machine is producing something.
No of Failures is the total no of breakdowns of the machine for a particular time period.
Calculation Example
Following is the data for a machine and we are going to calculate MTBF for a month.
| Element | Time |
| Duration of shift | 480 minutes |
| Total break duration per shift | 2 nos 15 minute tea breaks and 30 minute lunch break |
| Total downtime for the month | 1356 minutes |
| No of shifts scheduled per day | 3 |
| No of working days per month | 25 |
| Total no of failures for a month | 8 |
Now, let’s calculate…
Run time for that month = (((480 – (30+30)) x 25 x 3) – 1356
= 30144 minutes
MTBF = 30144 / 8
= 3768 minutes
In our example idle time of the machine is assumed nto be zero. If the machine have idle time, reduce idle time also from the available time.
How to interpret MTBF
MTBF can be used for analyzing the performance of the machine from the perspective of downtime.
For example, in our example MTBF for a particular month id 3768 minutes. Now we can compare the MTBF of this machine for previous months and analyze its performance.
If the MTBF of a particular machine is increasing from its previous months we can say its performing well and if its decreasing we can say its not performing well and we need to take actions to reduce down time.
We can also compare the MTBF with different machines of same kind.
Higher the MTBF better the machine.
Hope you got a idea of MTBF.
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What if i have 10 machines? will the available time get multiplied by 10?
Hi Meet…. I don’t recommend to calculate one mtbf for all machines together, since it only give a general idea of all machines….and by analysing that we cannot focus on improvement, where it is really needed.
It will give overall idea.
One thing we can do is first calculate individual mtbf and then calculate overall mtbf.
When calculating overall mtbf all times must be multiplied by no of machines or we should add up times of all machines.
ok, thanks melvin for clarifying this