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MTBF and MTTR calculator: availability and reliability
Enter the observed period, downtime and number of failures to get MTBF, MTTR, inherent availability and R(t), per EN 13306. Free, no sign-up.
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- Formula and standards shown
- On desktop and phone
Result
177.0hMTBF
- MTTR
- 3.00h
- Inherent availability D
- 98.33%
- Failure rate λ
- 0.005650 /h
- Reliability R(t)
- 0.3871
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What are MTBF and MTTR?
MTBF (mean time between failures) is the average operating time of a repairable item between two consecutive failures; MTTR is the average time needed to restore it after a failure. EN 13306 sets the maintenance terms behind both, and the IEC vocabulary (IEC 60050-192) reads the R of MTTR as restoration: the whole time from failure to restart, longer than the hands-on repair. Together they give inherent availability, MTBF / (MTBF + MTTR).
For the maintenance team, the two figures answer different questions. MTBF says how often a machine stops, and so whether the preventive plan or the design needs work; MTTR says how long each stop lasts, and so whether spare parts, documentation and skills are in place. On the packaging line of the example, 4 failures and 12 hours of downtime over 720 hours give an MTBF of 177 hours, an MTTR of 3 hours and an availability of 98.3%.
Operating time, not calendar time
MTBF counts the hours the machine was able to run. Leaving the downtime in the period inflates it, more so on a machine that fails often.
MTTF for parts you replace
A bearing or a fuse is not repaired, it is replaced: its indicator is the mean time to failure, MTTF. MTBF belongs to the machine that receives the new part.
A mean, not a promise
With a constant failure rate, the chance of running a full MTBF without failure is e^(−1), about 37%: roughly 63% of identical machines fail before reaching it.
Count failures the same way
Compare MTBF only between machines whose stops are logged by the same rules: decide once whether a short stop, or a defect found at inspection, counts as a failure.
Reference documents : EN 13306:2017, Maintenance terminology ; IEC 60050-192, Dependability vocabulary ; ISO 14224, Reliability and maintenance data collection
MTBF and MTTR filed with the work order
Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.
The CMMS software comparison, our gaps included- Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
- On the technician's phone, even without a network.
- In the machine's history, for the next breakdown.
When to calculate MTBF and MTTR
01
Compare two machines or two lines over the same period, with the same definitions (EN 13306).
02
Measure the effect of a reliability improvement: MTBF before and after, over periods of equal length.
03
Estimate the probability that a machine gets through a production run without a breakdown.
Good to know
R(t) assumes a constant failure rate (exponential law). For wear-out failures, which become more frequent with age, the Weibull distribution describes reality better.
MTBF formula, MTTR formula and availability
MTBF is the mean operating time between two failures, MTTR the mean time to repair. From the observed period, the downtime and the number of failures, the calculator derives inherent availability, the failure rate and the probability of running through a given mission time.
Formula · Reference documents
MTBF = (period − downtime)/N ; MTTR = downtime/N repairs ; D = MTBF/(MTBF + MTTR) ; λ = 1/MTBF ; R(t) = e^(−t/MTBF)
EN 13306 ; EN 15341 ; ISO 14224
Inputs and accepted ranges
| Input | Unit | Accepted range | Example |
|---|---|---|---|
| Data | 2 options | History | |
| Periodif Data: History | h | 0.01 to 10,000,000 | 720 h |
| Downtimeif Data: History | h | 0 to 10,000,000 | 12 h |
| Failuresif Data: History | 1 to 1,000,000 | 4 | |
| Repairsif Data: History | 1 to 1,000,000 | Optional | |
| MTBFif Data: Known MTBF and MTTR | h | 0.001 to 1,000,000,000 | |
| MTTRif Data: Known MTBF and MTTR | h | 0 to 10,000,000 | |
| Mission time t | h | 0 to 1,000,000,000 | 168 h |
Calculated results
- MTBFh
- MTTRh
- Inherent availability D%
- Failure rate λ/h
- Reliability R(t)
Breakdowns logged where MTBF starts: in Reglova
- Breakdowns reported by QR code
- Work orders on the phone, even without a network
- Mandatory inspections reminded by email
- Audit file as a PDF, in one click
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