MTBF & MTTR Calculator
The two numbers maintenance lives by: how long an asset runs before it fails, and how long it takes to fix. Together they give you availability. Updates as you type.
Your asset history
One asset over a defined window (e.g. last quarter).
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Cut MTTR by minutes, raise MTBF by months.
Most repair time is diagnosis: figuring out what broke and why. Fabrico records each stop and repair, so MTTR and MTBF build up per machine, and where cameras are fitted the video of a stop sits next to its machine data so the cause can be reviewed.
Book a Fabrico demo See how Fabrico tracks machine downtimeThe formulas
- MTBF = total operating time ÷ number of failures. Higher is better: the asset runs longer between failures.
- MTTR = total repair time ÷ number of failures. Lower is better: failures are fixed faster.
- Inherent availability = MTBF ÷ (MTBF + MTTR).
With 1,000 operating hours, 10 failures and 20 repair hours: MTBF = 100 h, MTTR = 2 h, availability = 100 ÷ 102 = 98.0%.
MTTR falls when the technician knows where to look first. The guides for the tablet press, blown film line, centrifugal pump and conveyor list symptoms, causes and fixes for their common faults.
A worked example: one filler, one month
A filler on a bottling line was scheduled for 600 hours in October. It stopped 8 times for failures and spent 12 hours in repair, so it ran 588 hours.
- MTBF = 588 h ÷ 8 failures = 73.5 h between failures.
- MTTR = 12 h ÷ 8 failures = 1.5 h per repair.
- Availability = 73.5 ÷ (73.5 + 1.5) = 98.0%, the same as 588 of 600 hours.
Two ways to win time back. Cut every repair by 30 minutes (MTTR 1.0 h) and the month gets 4 hours back, availability 98.7%. Prevent 2 of the 8 failures instead, with repairs still at 1.5 h, and it gets 3 hours back, 98.5%. Faster diagnosis often pays first, because it works on every failure, including the ones nobody has learned to prevent yet.
What counts as a failure, and what counts as repair time
- A failure is an unplanned stop that needs a repair, a part or a technician to reset it. Changeovers, planned maintenance and waiting for material are not failures: log them, but keep them out of MTBF.
- Short stops under your micro-stop threshold (a jam cleared in a minute) belong to performance in OEE, not to MTBF. Mixed in, they make MTBF look terrible and bury the real breakdowns. The hidden factory calculator shows what those short stops cost.
- Repair time runs from the stop to the restart if you track MTTR as time to restore, or covers only the hands-on minutes if you track wrench time. Pick one, write it on the report, keep it.
- Operating time is the time the asset was meant to run and did, not calendar hours. A machine on one shift cannot be compared with one on three by calendar time.
MTBF, MTTF and failure rate
MTBF is for assets you repair and put back to work: a pump, a filler, a press. MTTF (mean time to failure) is the same idea for parts you replace instead of repair, such as a bearing, a fuse or a lamp. The failure rate the calculator shows is 1 ÷ MTBF: 8 failures in 588 hours is about 0.0136 failures per hour.
Common mistakes
- One MTBF for the whole plant. It averages the good assets with the bad one and points nowhere. Calculate it per asset, then rank them.
- Too short a window. With two or three failures in the period, one more failure moves MTBF a lot. Use a quarter or longer for assets that rarely fail.
- Counting alarms, not stops. A fault that trips three times before it is fixed is one failure with a long repair if the machine never ran in between. Decide the rule once.
- No cause on the record. MTBF says how often, not why. Log a reason with every failure, or next month's number only improves by luck.
The free OEE tracker logs each stop with its reason and length, which gives you the failure count and the repair hours this calculator needs. For the step by step method, see how to calculate MTTR.
How do you calculate MTBF?
Divide operating time by the number of failures in the same period. 588 running hours and 8 failures give an MTBF of 73.5 hours.
How do you calculate MTTR?
Divide total repair time by the number of failures. 12 hours of repair across 8 failures is an MTTR of 1.5 hours. Say whether your repair time includes waiting for parts and people.
What is the difference between MTBF and MTTF?
MTBF is for equipment you repair and run again. MTTF is for parts you replace when they fail, such as bearings or fuses, where there is no time between failures on the same part.
Should MTTR include waiting time?
It depends on your definition. "MTTR (repair)" is wrench time only; "MTTR (restore)" includes waiting for parts and technicians. Be consistent and label which you use: the waiting is often a large, fixable chunk.
How does this relate to OEE?
Availability here is the reliability view of the same availability factor in OEE. Frequent short failures also overlap with micro-stops.
What's a good MTBF?
It's entirely asset- and context-specific. Compare against your own trend and similar equipment, not a universal number. The goal is the direction: MTBF up, MTTR down.
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