Templates and records · ISO 17025 · Clause 7.6

Calculating measurement uncertainty under ISO 17025

How far the result may lie from the true value, and why: the sources behind it, their size and the uncertainty that accompanies each report.

In one sentence

The measurement uncertainty calculation identifies the significant contributions, quantifies each one with its type of evaluation, combines them into the combined standard uncertainty and expresses it as an expanded uncertainty with its coverage factor, because clause 7.6 of ISO/IEC 17025 requires calibration laboratories to evaluate it for all their calibrations and testing laboratories to evaluate it or, where the method rules out a rigorous evaluation, to estimate it from the method’s principles or from experience.

Content reviewed on 17 October 2026

Where the standard requires it: ISO 17025 · Clause 7.6 Clauses are cited using the numbering of ISO/IEC 17025:2017, the current edition and the same one the Academy uses.
Type of information: Mandatory record Evaluation required by 7.6; its basis forms part of the technical records (7.5.1)
Who fills it in: Technical lead for the method With staff authorised for validation; reviewed by technical management
When: When the method is validated or verified Reviewed when the method or equipment changes or when control data point to it
How long it is kept: Set by the laboratory The standard requires a retention time to be defined for each record, consistent with contractual and legal obligations (8.4.2). Covering at least the accreditation cycle lets you show the history at every reassessment.

What the standard requires

What ISO 17025 demands and what it leaves to your judgement

The standard requires the contributions to uncertainty to be identified and all of them to be taken into account, including those from sampling where the laboratory samples, using appropriate methods of analysis.

A calibration laboratory evaluates the uncertainty of all its calibrations, including those of its own equipment. A testing laboratory evaluates it and, if the method precludes a rigorous metrological evaluation, estimates it based on theoretical principles or practical experience; where a standard method specifies values for the major sources and the form of presentation, following it is enough.

The standard does not impose a method. The GUM is the reference for the component-by-component approach; validation and quality control data support a global (top-down) approach, widely used in chemical testing.

Read it in context: Process requirements, in the ISO 17025 Academy

Structure

Fields the template should include

Method, measurand and range of application
Measurement model or approach used
Contributions identified and their origin
Value of each contribution, type of evaluation and distribution
Combined standard uncertainty
Coverage factor and level of confidence
Expanded uncertainty and how it is stated in the report
Supporting data: validation, quality control, proficiency testing
Review date

Example

Example: uncertainty budget for nickel in water

Company, people and figures are fictitious: the example only shows what a properly completed record looks like.

Field	Content
Method	Nickel by ICP-MS · range 5-500 µg/L
Approach	Global, using validation and internal quality control data
Intermediate precision	3.6 % · 12 months of control material
Bias	1.9 % · certified reference material and 4 proficiency tests
Calibration standards	1.0 % · supplier certificate
Combined	4.2 %
Expanded	8.4 % with k = 2, a level of confidence of approximately 95 %
In the report	50 ± 4 µg/L
Review	Annual · next in January 2027

At the audit

Mistakes auditors commonly flag

Uncertainty calculated once and never reviewed against control data.
Significant contributions overlooked, such as sample preparation.
Uncertainty reported at a different level of confidence from the one calculated.
Uncertainties smaller than the precision observed in quality control.
The decision rule ignores the uncertainty being reported.

In Kimobox

How this record is kept in Kimobox

1Each method is documented with its associated uncertainty, as a controlled document with versions.
2Internal quality control results are recorded with their trend on a dashboard and feed the uncertainty review.
3Results reports are generated from a controlled template in the system.

Frequently asked questions

What people ask us before getting started

Must uncertainty always be stated in the report?

Not always. ISO/IEC 17025 requires it in a test report when it is relevant to the validity or application of the result, when the customer asks for it or when it affects conformity with a limit. In calibration certificates it is always reported.

Which calculation method should be used?

The standard does not impose one. The GUM is the reference for the component-by-component approach; for testing, the global approach using validation, internal control and proficiency testing data is accepted if it is documented.

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Sources

Where each figure comes from

References to the official text in force. If a standard is revised, this page is updated and the review date says so.

ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories ISO/IEC · November 2017
JCGM 100:2008 — Evaluation of measurement data. Guide to the expression of uncertainty in measurement (GUM) BIPM / JCGM · 2008 edition
ILAC G8 — Guidelines on Decision Rules and Statements of Conformity ILAC · Edition 09/2019