What this calculator does
MTTR measures the average active duration required to diagnose, repair, test, and restore equipment after a qualifying failure. It is a maintainability measure, not necessarily total downtime.
When to use it
Use it to trend repair execution, assess access or diagnostic improvements, and pair with MTBF for inherent availability. State whether troubleshooting, testing, or travel time is included.
Inputs and formula
Total active repair time is summed across completed repairs. MTTR = total active repair time ÷ completed repairs
Worked example and interpretation
40 active repair hours across 10 repairs gives an MTTR of 4 hours. A fall in MTTR can reflect better maintainability, parts staging, skills, or simply a different mix of failures.
Practical notes and limitations
Do not silently mix wrench time with full outage time. Waiting for access, permits, technical support, or material is operational delay and may deserve a separate measure. Use backlog and parts data to explain those delays.