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MTBF And MTTR Calculator

Work out mtbf and mttr instantly with clear inputs, formula shown and shareable results.

About MTBF And MTTR Calculator

Availability is MTBF divided by MTBF plus MTTR, so it improves either by failing less often or by recovering faster — and recovery is usually the cheaper lever. Parallel redundancy compounds the result: two units each at 99.9 percent give 99.9999 percent provided their failures are genuinely independent.

Formula

Availability from MTBF and MTTR

MTBF = operating hours / failures; MTTR = repair hours / failures; A = MTBF / (MTBF + MTTR); with N units A = 1 - (1 - A)^N

Worked example

With the default values below, MTBF And MTTR Calculator returns Mean time between failures of 7,300. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total operating hoursminimum 1 h
43,800 h
Number of failuresminimum 1
6
Total repair timeminimum 0 h
18 h
Units in parallelaccepts 1–10
2

Results

Mean time between failures
7,300 h
Mean time to repair
3.00 h
Availability of one unit
99.9589%
Availability with redundancy
99.99998%

Step by step

  1. 1Values used
  2. 2Availability from MTBF and MTTR
  3. 3Mean time between failures= 7,300 h
  4. 4Mean time to repair= 3.00 h
  5. 5Availability of one unit= 99.9589
  6. 6Availability with redundancy= 99.99998

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Which is easier to improve, MTBF or MTTR?

MTTR, almost always. Hardware reliability is largely fixed by the vendor, while spares on site, documented procedures and automated failover can cut repair time by an order of magnitude.

Why is redundant availability often worse than the maths predicts?

Because failures correlate. Shared power, shared firmware bugs and a common cooling failure defeat the independence assumption entirely.

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