This free MTBF calculator turns your breakdown records into the two classic maintenance KPIs: mean time between failures (MTBF) and mean time to repair (MTTR). It also calculates availability from these two values, so you can see whether your machine loses more time because it fails often or because repairs take long.
Free MTBF Calculator
Use one machine and one period, for example the last three months. Count only unplanned failures and list them by failure mode with their total repair time. Add a mission time (such as one shift) to get the probability of running it without a failure, and optionally split the average repair into waiting, diagnosis, spare parts, repair and restart to see where MTTR really goes. The result exports to Excel with live formulas.
MTBF, MTTR & Availability Calculator
Pro · freeKey takeaways
- MTBF = operating time ÷ number of failures – higher is better.
- MTTR = total repair time ÷ number of repairs – lower is better.
- Availability = MTBF ÷ (MTBF + MTTR).
- Frequent short failures and rare long failures need different countermeasures.
MTBF and MTTR Formulas
| KPI | Formula | Improve by |
|---|---|---|
| MTBF | Total operating time ÷ number of failures | Preventive maintenance, root cause elimination, better design |
| MTTR | Total repair time ÷ number of repairs | Spare parts, skills, diagnostics, standard repair procedures |
| Availability | MTBF ÷ (MTBF + MTTR) | Both of the above |
Operating time excludes planned stops such as breaks and planned maintenance. MTTR usually includes the whole downtime from failure to restart: waiting for the technician, diagnosis, waiting for parts, repair and test.
Worked Example
A welding machine ran 1,200 hours in a quarter, had 15 breakdowns and 30 hours of total repair time.
- MTBF = 1,200 ÷ 15 = 80 hours – about one failure every ten 8-hour shifts.
- MTTR = 30 ÷ 15 = 2 hours per failure.
- Availability = 80 ÷ 82 = 97.6%.
The team breaks the 2 hours down: 50 minutes are spent waiting for a technician and parts. Cutting that waiting time is faster and cheaper than any redesign.
How to Increase MTBF
- Rank failure causes with a Pareto chart and attack the top ones.
- Introduce operator-led cleaning, inspection and lubrication – the core of TPM.
- Base preventive maintenance intervals on real failure data.
- Use the 5 Whys for every repeated breakdown.
How to Reduce MTTR
- Keep critical spare parts at the machine or in a known location.
- Create one-page repair standards with photos.
- Train operators for first-level fixes – plan coverage with a skills matrix.
- Use andon signals so technicians are called immediately.
MTBF, MTTR and OEE
Breakdowns are part of the availability loss in OEE. MTBF and MTTR explain the “why” behind a low availability number: too many failures or too slow repairs.
MTBF Calculator FAQ
What is a good MTBF?
There is no universal value – it depends on the machine type and duty cycle. Compare a machine with its own history and with similar machines in your plant.
What is the difference between MTBF and MTTF?
MTBF applies to repairable equipment. MTTF (mean time to failure) is used for non-repairable items such as bearings or electronic components.
How do you calculate MTBF when a machine has had no failures?
You cannot calculate a meaningful MTBF with zero failures. Report the operating hours without failure instead, or extend the observation period. Some reliability methods estimate a lower confidence limit for MTBF in this case, but for shop-floor decisions a longer data period is usually more useful.
Next Steps
Export last quarter’s breakdown data for your bottleneck machine and run the MTBF calculator. For definitions, see the OEE.com glossary.