MTBF, MTTR & availability calculator
Calculate operating hours between failures, average repair time, and repair-based availability from one consistent event window.
Result
Inputs used
- Total operating time (hours)
- 1000
- Completed failure events
- 5
- Total repair downtime (hours)
- 20
| MTBF | 200 hours/failure |
|---|---|
| MTTR | 4 hours/failure |
| Repair-based availability | 98.039216 % |
This repair-based estimate excludes logistics delays, scheduled maintenance and other downtime unless included in your repair definition. MTBF is not a lifetime guarantee.
From the maintainer: Understanding the Shop Floor — a practical companion to the systems behind these tools; also How to Remain Valuable When Intelligence Becomes Cheap — on staying valuable as AI and automation reshape engineering work.
Formula and worked example
MTBF = total operating hours / failures. MTTR = total repair downtime / completed repair events. With one completed repair per failure, repair-based availability = MTBF / (MTBF + MTTR).
For 1,000 operating hours, five failures and 20 repair hours, MTBF is 200 hours, MTTR is 4 hours, and repair-based availability is 98.0392%. The same availability follows from 1,000 / (1,000 + 20).
Keep event definitions consistent
Use operating time, not elapsed calendar time, in the MTBF numerator. Include only a consistent population of assets and failures. State whether repair time includes diagnosis, spares, permits and restart. If some events are unfinished, do not silently treat their missing repair duration as zero.
This is a descriptive estimate over the entered observation window. It does not establish a constant failure rate or predict an individual component's remaining life. Scheduled work and waiting time need a separate operational-availability calculation when excluded from repair time.
Frequently asked questions
What if there were no failures?
The tool requires at least one event. A failure-free observation is useful evidence but does not support reporting an infinite MTBF as a measured reliability claim.
Can MTBF tell me when to replace equipment?
No. Replacement decisions also need failure modes, age, condition, consequences and uncertainty.
Reference
NIST: constant repair-rate model discusses total operating time divided by failures and the model assumptions behind inference.
Go deeper
Cite this page: MTBF, MTTR & availability calculator
, Shopfloor. https://shopfloor.space/tools/mtbf-mttr-calculator/