Glossary
MTBF & MTTR in manufacturing: reliability vs recovery speed
MTBF measures how long a machine runs before it breaks down. MTTR measures how fast it gets fixed once it does. Different questions, usually tracked together.
Updated October 2026 · ThingConnect team
Two different questions
MTBF (Mean Time Between Failures) asks how long a machine runs before something stops it. MTTR (Mean Time To Repair) asks how long it takes to get running again once it does. A machine can have excellent MTBF and terrible MTTR — rarely breaks down, but a four-hour wait for the right spare part when it does — and the two numbers point maintenance in completely different directions.
A worked example
One machine, one calendar month, 680 running hours:
Total running hours
- Value
- 680 hrs
Breakdowns in the month
- Value
- 4
Total repair time across those 4 breakdowns
- Value
- 12 hrs
| Input | Value |
|---|---|
| Total running hours | 680 hrs |
| Breakdowns in the month | 4 |
| Total repair time across those 4 breakdowns | 12 hrs |
MTBF = 680 ÷ 4 = 170 hours between failures. MTTR = 12 ÷ 4 = 3 hours average repair time. Read together: this machine fails roughly once a week of running time, and each failure costs about half a shift to fix — two separate levers, and two separate conversations with two different teams.
Why both numbers, not just one
A plant chasing only MTBF ends up over-investing in prevention for a machine whose actual problem is slow repairs (missing spares, undocumented fault codes). A plant chasing only MTTR optimizes repair speed on a machine that would be better served by not failing in the first place. Reading both per machine — not as a plant-wide average, which hides which specific machine is driving the number — is what points at the right fix. See the full predictive maintenance picture for what changes once a machine's failure pattern is actually visible.
Run your own numbers in the MTBF calculator and the MTTR calculator.
Questions
Frequently asked questions
MTBF stands for Mean Time Between Failures — the average run time between breakdowns. MTTR stands for Mean Time To Repair — the average time it takes to fix a machine once it fails. One measures reliability, the other measures recovery speed.
A higher MTBF means fewer breakdowns, which is almost always good — but it's only meaningful measured per machine, over a consistent window. A single long breakdown-free stretch after a major overhaul isn't yet a trend; MTBF becomes useful once you're comparing the same machine's rolling average month over month.
Not in practice — a low MTTR just means fast, competent repairs. What's worth watching is MTTR trending up on a specific machine, which usually means spares aren't on hand, the failure mode is unfamiliar, or diagnosis is taking longer than the actual repair.
Both need two inputs the controller already has: when the machine stopped and when it started again. Reading machine state directly gives exact stop/start timestamps per event, which is what the formulas below actually need — a manual log usually rounds to the nearest 5 or 10 minutes, which matters less for MTBF's longer intervals but can meaningfully skew MTTR on short repairs.