Mean time to repair, written MTTR, is the average time it takes to get a machine back into production after a failure. The formula is MTTR = total repair time divided by number of repairs. Repair time is measured from the moment the machine stops until it is running good product again.
That window includes more than wrench time. It covers finding the technician, diagnosing the fault, fetching parts, doing the repair, and restarting the machine. If the real delay is a two-hour wait for a spare, that belongs in the number, because the line was down for those two hours. Leaving it out hides the problem you most need to fix.
MTTR tells you something different from MTBF. A machine can fail rarely but take a full shift to repair, or fail often but be back in three minutes. You need both numbers to understand how much production you are losing and where the fix should go: fewer failures, faster repairs, or both.
Standard Procedure
- 1For each failure, record the stop time and the time good product resumed.
- 2Calculate each repair duration and note the biggest single contributor (diagnosis, parts, repair, restart).
- 3Add the durations and divide by the number of repairs.
- 4Review the longest repairs for delays that a spare part or a checklist could remove.
Lesson Summary
- ✓MTTR covers the whole stop, not just the time a technician held a tool.
- ✓Long waits for parts or diagnosis are the easiest MTTR wins.