Project Details Guidelines for the derivation of values and uncertainties from standard atomic weight intervals

Project No.:
Start Date:
01 September 2013
End Date:
30 April 2021


The introduction of the interval notation for expressing the standard atomic weight for selected elements has raised questions in the measurement community on how to use these in practical calculations which require a single value and the associated uncertainty. The objective of the project is to establish joint IUPAC-JCGM guidelines for the interpretation and use of the atomic weight intervals in practical situations.

The proposed project is complementary to the active IUPAC project 2011-040-2-200 which focuses on how to use existing CIAAW recommendations to obtain tailored atomic-weight values of the elements from specified sources, such as the air or seawater.


The project will, based on existing publications concerning the standard atomic weights and the isotopic composition of terrestrial materials to make a probabilistic interpretation of the atomic weight intervals.

Three of the task group (Adriaan van der Veen, Antonio Possolo, and D. Brynn Hibbert) are members of JCGM-WG1, the working group that is concerned with the Guide to the expression of uncertainty in measurement (GUM) and its supplements, and the approach taken will reflect the most current thinking on modelling of measurements and in particular measurement uncertainty.

Task group member Juris Meija secretary of the CIAAW and member of IUPAC project 2011-040-2-200 and will provide liaison with these groups.

A mise en pratique will be prepared to explain the calculation of a standard atomic weight and uncertainty for elements and substances.


Nov 2014 – Project announcement published in Chem. Int. Nov-Dec 2014, p. 20; DOI: 10.1515/ci-2014-0616

August 2015 update – Two publications are currently under review by the TG members and associated experts.

April 2016 update – The provisional recommendations titled “Guidelines for the Derivation of Values and Uncertainties from Standard Atomic Weight Intervals” is available for public till 31 Aug 2016.

Feb 2018 update – A Technical Report titled “Interpreting and propagating the uncertainty of the standard atomic weights” has been published in Pure and Applied Chemistry, 90(2), pp. 395-424, 2018; AOP 4 Jan 2018;

May 2021 update –  A Technical Report titled “Interpretation and use of standard atomic weights (IUPAC Technical Report)” has been published in Pure and Applied Chemistry, AOP 26 Apr 2021;

project completed

Page last updated: 25 May 2021