MTBF, Failure Rate and Reliability Calculator
Convert between mean time between failures, failure rate and FIT, and estimate the probability that equipment works without failure for a given time.
- λ = 1 ÷ MTBF, FIT = λ × 10⁹
- R(t) = e−λt = e−0.0876 = 91.61 %
Reliability Formulas
R(t) = e−λt
Assumes a constant failure rate (the flat part of the bathtub curve), which suits electronics during useful life but not wear out items.
Worked example
An MTBF of 500,000 h is λ = 2 × 10⁻⁶ /h = 2000 FIT. Over 5 years (43,800 h) the reliability is e−0.0876 = 91.6 %.
Frequently Asked Questions
What is FIT?
Failures in time: the number of failures per 10⁹ device hours. 1000 FIT equals an MTBF of 1 million hours.
Is MTBF the same as MTTF?
MTTF applies to non repairable items, MTBF to repairable ones; with a constant failure rate both equal 1/λ.
How do I combine failure rates?
For components in series (all needed), add the failure rates.
Learn more on the blog
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