The values that can be used in cases where the source and isotopic composition of a particular sample is unknown are referred to as "conventional atomic weight” values. Remember that, even though a single number is listed for conventional atomic weights, these values do not imply that the atomic weight values are constant in all cases. These values should be used for calculations that do not specify isotopic compositions or when the source or the material is unknown. They are also used for some commercial purposes.

These values are listed below for the elements that belong in category one, as of 2015.