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MTBF and MTTR calculator
MTBF (mean time between failures) = uptime / number of failures. MTTR (mean time to repair) = failure downtime / number of failures. Availability = MTBF / (MTBF + MTTR). A machine planned for 160 hours with 4 failures and 8 hours of repairs has an MTBF of 38 hours, an MTTR of 2 hours and 95% availability. Enter your numbers, or take the failures and repair time from the downtime log. Morsa keeps these numbers current from the machines and the shift chat, so nobody has to count stops.
Updated October 21, 2026
The formulas
Uptime = planned run time - downtime from failures.
MTBF = uptime / number of failures. It measures reliability: how long the machine runs before it stops.
MTTR = downtime from failures / number of failures. It measures maintainability: how fast it gets back up.
Availability = uptime / planned run time = MTBF / (MTBF + MTTR).
Failure rate = 1 / MTBF, failures per run hour.
The IEC dependability vocabulary (IEV 192) defines these terms; in maintenance the R in MTTR usually covers the whole time from the stop to running again, not only the wrench time. Use the same rule every time you measure.
Worked example
| Input or result | Value | How |
|---|---|---|
| Planned run time | 160 h | two shifts, 5 days, 2 weeks |
| Failures | 4 | unplanned stops |
| Failure downtime | 8 h | total repair time |
| Uptime | 152 h | 160 - 8 |
| MTBF | 38 h | 152 / 4 |
| MTTR | 2 h | 8 / 4 |
| Availability | 95% | 38 / (38 + 2) |
Some articles divide planned time, not uptime, by the failures and get 40 hours here. That overstates MTBF by exactly one MTTR, which matters on machines that take hours to fix. This calculator uses uptime.
MTBF vs MTTR vs MTTF
| Metric | Answers | Improve it with |
|---|---|---|
| MTBF | How often does it break? | Preventive maintenance, root cause fixes, better setups |
| MTTR | How long to get it back? | Spare parts at the machine, clear work orders, trained people, fast diagnosis |
| MTTF | How long does a part last before it is replaced (not repaired)? | Better parts; used for bearings, belts, sensors |
Using the log
On the machine downtime log, every unplanned stop counts as a failure and its minutes as repair time; planned codes (PM, changeover, breaks) are left out. Pick a machine here and the calculator fills in both numbers. Enter the planned hours for the same period yourself.
The modern way: the log writes itself
Paper logs and spreadsheets fail the same way: the stop happens at 2 AM, the note gets written at the end of the shift, if at all, and the reason says “machine down”. Plants that run an AI operations agent such as Morsa stop asking operators to fill in forms. Overnight, Lathe 6 is down 40 minutes. Morsa takes the alarm code from the machine and the operator’s note from the shift chat (“chips wrapped on bar feeder”), codes it, sends maintenance a work order for tonight and asks the tool room for chip breaker inserts. It is the third time this week, so the machine builder’s service team gets an email with the alarm log attached. The 6 AM brief shows the 40 minutes with its reason, and the fix is already moving. People approve; nobody retypes.
Common questions
What is a good MTBF?
There is no single number: compare a machine with itself over time, and machines of the same kind with each other. A rising MTBF and a falling MTTR on your worst machine is the goal.
What if there were no failures?
MTBF cannot be computed from zero failures; the calculator says MTBF is at least the run time and asks for a longer period.
Do changeovers count as failures?
No. Changeovers and preventive maintenance are planned. They reduce availability in OEE but are not failures in MTBF.
Related tools
WHERE MORSA FITS
When a machine stops, the reason and the fix should already be moving.
Morsa reads the alarm from the machine and the operator’s note from the shift chat, codes the stop, opens the work order, asks the tool room for parts and, on the third stop in a week, emails the machine builder with the alarm log. It works in Teams, WhatsApp, email or whatever your floor already uses.
