Weibull reliability calculator

β under 1 means a decreasing failure rate (infant mortality: defects that show up early). β near 1 means a constant failure rate, which is the exponential distribution. β over 1 means wear-out, and the higher it is, the more failures bunch up around the same age.

The characteristic life: the age by which 63.2% of units have failed, whatever the shape. It sets the time scale; β sets the shape.

The age by which 10% of units are expected to fail: η × (−ln 0.9)^(1/β). Bearing and component makers often quote B10 instead of MTTF because it describes the early tail customers notice.

MTTF = η × Γ(1 + 1/β). It equals η only when β = 1. For β = 2, MTTF ≈ 0.886 η.

Fit failure times on a Weibull probability plot or with maximum-likelihood software. The slope of the plot is β and the 63.2% point is η. This calculator takes the fitted values and answers the reliability questions.

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