Understanding MTBF
How we calculate. MTBF = cumulative operating/uptime ÷ number of failures. The form uses the same arithmetic as the worked examples on this page. See our methodology and accuracy policy.
Real-world scenario: A typical MTBF case uses total uptime 8640 and failures 6. Enter the same figures below to reproduce the worked path.
What is MTBF?
A reliability metric distinct from MTTR (restore speed) and MTTD (detect speed). Higher MTBF means failures are less frequent.
- Uptime = operating time in the window
- Failures = countable outages/faults per policy
- Same unit for the result as uptime
The Formula
Worked Example
Common Use Cases
- Hardware/fleet reliability: failure spacing
- Service health: how often it breaks
- Capacity planning: expected failure cadence
Pro Tips
- Define failure consistently
- Don’t mix planned reboots unless intentional
- Use with availability %
Limitations: MTBF results are educational DevOps/SRE/FinOps planning aids—not SLAs, billing guarantees, or operational policy. Confirm definitions with your platform and finance teams.
FAQ
MTBF vs MTTR?
MTBF is time between failures; MTTR is average time to restore after a failure.
What if failures is 0?
MTBF is undefined for a zero-failure sample—use a longer window or report “no failures.”
Authoritative References
For SRE and FinOps definitions, consult:
- Google SRE books — SLOs, error budgets, toil
- DORA — delivery performance research
- FinOps Foundation — cloud cost practices