Reliability calculators
Three everyday tools for the reliability engineer — 100% in your browser: no data leaves this page.
Guide — How to use
The theory behind the three tools, what each parameter actually is, where the data comes from and how to read the results. Not everyone carries this by heart — that is what this guide is for.
2-parameter Weibull
Fw A reading: Wear-out (β>1)chance of passing 500 h without failing
share already failed by 500 h
risk of failing in the next hour
mean life to failure
age at which 10% of the population has failed
R(t)
h(t)
R(t) = exp(−(t/η)^β) · h(t) = (β/η)·(t/η)^(β−1). Validated against Smith (2004) and known properties (R(η)=e⁻¹). The note's editorial category prevails over this didactic reading.
MTBF · MTTR · Availability
share of time fit for duty (technical repair only)
failure frequency (λ = 1/MTBF)
expected downtime hours per year
Ai = MTBF/(MTBF+MTTR) — inherent availability (Smith 2004, ch. 2). Reference year: 8760 h.
P-F interval
Adequatemaximum inspection interval (P-F/2)
possible detections before failure
route slack — negative = cannot get there in time
An on-condition task is only effective if inspection fits the P-F window — consecrated practice: inspection ≤ P-F/2 (Moubray, RCM II ch. 8).