Measurement, Test & Control Equipment worked example

Measurement Uncertainty Margin at 18% target uncertainty-to-tolerance ratio: a worked example

This worked example runs the measurement uncertainty margin numbers for a tougher week than the baseline: 18% target uncertainty-to-tolerance ratio instead of the typical 25%. Calculate the guard band or uncertainty margin between your measurement system uncertainty and the product tolerance. Determine if your measurement capability provides adequate decision confidence for pass/fail testing.

The inputs for this scenario

  • Expanded measurement uncertainty (U): 12 units (held at the documented default)
  • Total specification tolerance band: 100 units (held at the documented default)
  • Target uncertainty-to-tolerance ratio: 18 % (the input this scenario stresses; the baseline uses 25)

Working through the calculation

  • The calculation starts from the formula this tool documents: Uncertainty margin = expanded uncertainty / total tolerance band x 100.
  • Uncertainty-to-tolerance ratio works out to 12 % at these inputs, and this is the headline figure for the scenario.
  • Gap to target ratio works out to 6 points at these inputs.
  • Expanded uncertainty (U) works out to 12 count at these inputs.
  • Total tolerance band works out to 100 count at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where target uncertainty-to-tolerance ratio sits at 25% and the headline result is 12 %, this scenario lands almost exactly on the baseline at 12 %.
  • Use it when selecting a gauge for a feature, reviewing a calibration certificate against a part spec, or building a guard-banding decision for accept/reject at spec limits. 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

  • Uncertainty-to-tolerance ratio: 12 % (headline result)
  • Gap to target ratio: 6 points
  • Expanded uncertainty (U): 12 count
  • Total tolerance band: 100 count

Run it with your numbers

  • To rerun this with your own numbers, open the live Measurement Uncertainty Margin calculator, set target uncertainty-to-tolerance ratio to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.