Reliability — Cheat Sheet
Failure rate, MTBF, series/parallel, availability, Weibull and FIT.
Basics (constant λ)
| Reliability | R(t) = e^(−λt) = e^(−t/MTBF) |
| Failure rate | λ = 1 / MTBF |
| Unreliability | F(t) = 1 − R(t) |
| FIT | failures per 10⁹ hours |
Systems
| Series | R = ΠRᵢ, λ = Σλᵢ |
| Parallel (n) | R = 1 − Π(1 − Rᵢ) |
| k-out-of-n | binomial sum of R |
Availability
| Steady-state | A = MTBF / (MTBF + MTTR) |
| MTTF | mean time to failure (non-repairable) |
| MTBF | MTTF + MTTR (repairable) |
Weibull
| Reliability | R(t) = e^(−(t/η)^β) |
| Shape β | <1 infant, =1 random, >1 wear-out |
| Char. life η | R(η) = 0.368 |
| B10 life | t at R = 0.90 |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.