Reliability · Availability
MTBF MTTR availability calculator.
Estimate availability as MTBF divided by MTBF plus MTTR, and see the repair time you can afford for a target.
Inputs
Result
Enter the values above.
MTBF, MTTR and availability
AWS's Well-Architected Reliability Pillar gives the estimate Avail = MTBF / (MTBF + MTTR) for a component whose maker publishes no availability. Its example: an MTBF of 150 days and an MTTR of 1 hour gives 99.97%. Rearranged, the longest repair time that still meets a target availability A is MTTR = MTBF x (1 - A) / A.
Both inputs are averages over history, so the result is an estimate, not a guarantee. Cutting MTTR (faster detection, rollback, failover) often raises availability as much as stretching MTBF.
Frequently asked questions
How do I calculate availability from MTBF and MTTR?
MTBF divided by the sum of MTBF and MTTR. 150 days and 1 hour gives 99.97%.
What MTTR do I need for 99.9%?
About 0.1% of the cycle: with an MTBF of 30 days, MTTR must be under about 43 minutes.
What is the difference between MTBF and MTTR?
MTBF is the average time a system runs between failures; MTTR is the average time to recover from one.
Does MTTR include detection time?
It should for availability, because the service is down until it is restored. Define it consistently.
Sources
Checked
- AWS Well-Architected Reliability Pillar: Availability
- Google SRE Book: Appendix A, Availability Table
Formulas follow the sources above. Periods use a 30-day month and a 365-day year. Runs entirely in your browser; nothing you type is sent or stored.
Scope
Planning estimates only. Your SLA contract defines its own measurement window, exclusions and remedies, and those override these generic figures. Theoretical availability assumes independent failures.