Reliability Availability from MTBF and MTTR Calculator
This standard approximation relates average failure-free operating time to repair duration. It describes a simplified steady-state model rather than measured uptime for a specific calendar period.
How to use this calculator
- Enter mean time between failures (hours), mean repair time (hours) using the same measurement window and units.
- Check the result and intermediate values, then change one input at a time when comparing scenarios.
- Keep the stated scope and assumptions attached to any result you share.
Formula and method
Availability ≈ MTBF ÷ (MTBF + MTTR) × 100.
- The estimated steady-state availability is about 99.784%.
- This assumes the MTBF and MTTR are comparable and that the simplified renewal model is appropriate. Real service availability also includes detection, planned maintenance and dependencies.
Worked examples
Worked example
MTBF of 1,500 hours and MTTR of 3.25 hours.
The estimated steady-state availability is about 99.784%.
The estimated steady-state availability is about 99.784%.
Understanding the result
The estimated steady-state availability is about 99.784%.
This assumes the MTBF and MTTR are comparable and that the simplified renewal model is appropriate. Real service availability also includes detection, planned maintenance and dependencies.
Important notes
This assumes the MTBF and MTTR are comparable and that the simplified renewal model is appropriate. Real service availability also includes detection, planned maintenance and dependencies.
Use measured inputs or documented assumptions, and validate important decisions with the appropriate source specifications or professional guidance.
Frequently asked questions
Is this identical to measured uptime?
No. Measured uptime uses a defined observation window; this calculation estimates availability from failure and repair averages.
Can planned maintenance be included?
It can be tracked separately or included only if your operational definition says so.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.