Environmental Test Chambers & Reliability Labs worked example

Failure Rate Estimate at 2.3% allowable failure-rate target: a worked example

What does the result look like when allowable failure-rate target reaches 2.3%? The full calculation is worked below with real intermediate numbers. a reliability engineer needs a quick observed failure rate from completed testing

The inputs for this scenario

  • Samples failed during test: 3 samples (unchanged)
  • Total samples tested: 180 samples (unchanged)
  • Allowable failure-rate target: 2.3 % (raised for this scenario; the documented default is 2)

Working through the calculation

  • Applying the documented formula (Observed failure rate = samples failed during test ÷ total samples tested × 100) to the inputs above produces each figure below.
  • At this operating point the engine returns 1.67 % for observed reliability test failure rate, the number this scenario is built around.
  • At this operating point the engine returns 0.63 points for failure-rate gap to target.
  • At this operating point the engine returns 3 samples for samples failed during test.
  • At this operating point the engine returns 180 samples for total samples tested.

How this compares with the baseline

  • Against the tool's baseline example, where allowable failure-rate target sits at 2% and the headline result is 1.67 %, this scenario lands almost exactly on the baseline at 1.67 %.
  • A figure at this level is achievable when allowable failure-rate target is genuinely sustained, not just peaked for a shift. A raw failure rate from a small sample is a point estimate, not a confidence-bounded reliability figure - 3 of 180 looks like 1.67% but the true rate could be meaningfully higher; use a binomial confidence interval for go/no-go on critical lots.

Results at a glance

  • Observed reliability test failure rate: 1.67 % (headline result)
  • Failure-rate gap to target: 0.63 points
  • Samples failed during test: 3 samples
  • Total samples tested: 180 samples

Run it with your numbers

  • Every input above is editable in the live Failure Rate Estimate calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.