# Measurement uncertainty

> Measurement uncertainty is a parameter, usually stated as an expanded uncertainty at a 95 percent confidence level (k = 2), that characterises the range of values within which the true value of a measured quantity is expected to lie.

- Source: https://amps.global/glossary/measurement-uncertainty/
- Type: Glossary
- Published: 2026-09-05
- Tags: quality, calibration

## Key facts

- Evaluated per the Guide to the Expression of Uncertainty in Measurement (GUM, JCGM 100)
- ISO/IEC 17025 requires laboratories to evaluate uncertainty and report it when relevant to validity or when the client asks
- Calibration certificates state uncertainty; it propagates into thickness readings and flaw sizing
- Decision rules (how uncertainty is applied to an acceptance limit) must be agreed and stated

Also known as: uncertainty of measurement, expanded uncertainty, GUM.

## Why it matters in NDT

A remaining wall of 6.1 mm against a 6.0 mm minimum is a pass only if the uncertainty of the reading is understood. Inspection companies accredited to ISO/IEC 17025 or reporting measurements under ISO/IEC 17020 need a defensible statement of uncertainty for quantitative results.

## In AMPS

Uncertainty statements and decision rules belong in your procedures and report templates; AMPS reproduces them exactly because reports are generated from your own Word templates, and the calibration certificates that feed the uncertainty budget are filed on the equipment page.

## Related pages

- [Calibration certificate](https://amps.global/glossary/calibration-certificate/)
- [Ultrasonic thickness gauging](https://amps.global/glossary/ultrasonic-thickness-gauging/)
- [ISO/IEC 17025](https://amps.global/glossary/iso-iec-17025/)

## Sources

- [Measurement uncertainty on Wikipedia](https://en.wikipedia.org/wiki/Measurement_uncertainty)
- [ISO/IEC 17025:2017 at iso.org](https://www.iso.org/standard/66912.html)