Key takeaways
Short answer: MTBF measures reliability — how long an asset typically runs between failures. Availability measures uptime — the share of scheduled time it is actually running. They are linked but distinct: an asset with great MTBF but slow repairs (high MTTR) can still have poor availability. Availability depends on both how often it fails and how fast you recover. See also plant availability vs equipment availability.
Mean time between failures is a pure reliability metric: on average, how long does the asset run before it fails. It says nothing about how long the repair takes — only how frequently failure occurs. You raise it by eliminating the causes of failure.
Availability is the uptime metric: the share of scheduled time the asset is actually producing. It depends on two things — how often it fails (MTBF) and how fast you fix it (MTTR) — and it is the term that feeds OEE.
Availability equals MTBF divided by (MTBF plus MTTR). Raise MTBF (fail less) or cut MTTR (repair faster) and availability rises. Focus on only one and the other can quietly hold you back — which is why the two numbers must be read together.
An asset has a superb MTBF of 500 hours — it almost never fails. But when it does, the repair takes 50 hours because the spare is long-lead and the failure is hard to diagnose. Availability is 500 / (500 + 50) = 91%. A second asset fails more often (MTBF 100 hours) but is repaired in two hours: availability 100 / 102 = 98%. The "more reliable" asset has worse availability, because reliability without fast recovery is only half the picture.
An asset that rarely fails but takes a day to fix when it does can still have mediocre availability. Reliability and maintainability both matter, so track MTBF and MTTR together — improving failure frequency and recovery speed are different programs with different owners.
1. Optimising MTBF alone. Slow repairs still drag availability down.
2. Optimising MTTR alone. Frequent failures still cost uptime even if each is quick.
3. Confusing the two metrics. Reporting reliability as if it were availability.
4. Ignoring spare lead time. The biggest MTTR driver is often the part, not the labour.
Availability is one of OEE's three terms, and MTBF and MTTR are the levers beneath it: reliability engineering raises MTBF, faster response cuts MTTR, and OEE Availability climbs from both. Reading them together tells you which lever to pull.
Fabrico captures failures and repair times, so MTBF, MTTR and Availability are visible together and you can see which one is limiting uptime. Book a demo to see the reliability levers behind your OEE.
No — MTBF is reliability (how often it fails); availability also depends on repair speed.
Availability equals MTBF divided by (MTBF plus MTTR).
Yes — if repairs are slow, a rarely-failing asset can still have poor uptime.
Availability — driven by both MTBF and MTTR.
Often spare-part lead time, not the repair labour itself.
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