Environmental Test Chambers & Reliability Labs worked example

Failure Rate Estimate at 1.44% allowable failure-rate target: a worked example

This worked example runs the failure rate estimate numbers for a tougher week than the baseline: 1.44% allowable failure-rate target instead of the typical 2%. Calculate observed test failure rate from failed samples, total samples tested, and the allowable failure-rate target.

The inputs for this scenario

  • Samples failed during test: 3 samples (held at the documented default)
  • Total samples tested: 180 samples (held at the documented default)
  • Allowable failure-rate target: 1.44 % (the input this scenario stresses; the baseline uses 2)

Working through the calculation

  • The calculation starts from the formula this tool documents: Observed failure rate = samples failed during test ÷ total samples tested × 100.
  • Observed reliability test failure rate works out to 1.67 % at these inputs, and this is the headline figure for the scenario.
  • Failure-rate gap to target works out to -0.23 points at these inputs.
  • Samples failed during test works out to 3 samples at these inputs.
  • Total samples tested works out to 180 samples at these inputs.

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 %.
  • Use it at the end of a reliability or environmental test run when you have a final failed count and a defined acceptance criterion (AQL, lot tolerance, or design target). A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Observed reliability test failure rate: 1.67 % (headline result)
  • Failure-rate gap to target: -0.23 points
  • Samples failed during test: 3 samples
  • Total samples tested: 180 samples

Run it with your numbers

  • To rerun this with your own numbers, open the live Failure Rate Estimate calculator, set allowable failure-rate target to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.