Editing Avogadro constant (section)

=== SI redefinition of 2019 ===
{{main|2019 revision of the SI}}
In its 26th Conference, the BIPM adopted a different approach: effective 20 May 2019, it defined the Avogadro constant {{math|''N''{{sub|A}}}} as the exact value {{val|6.02214076|e=23|u=mol-1}}, thus redefining the mole as exactly {{val|6.02214076|e=23}} constituent particles of the substance under consideration.<ref name=cipm106/><ref name=NIST2019/> One consequence of this change is that the mass of a mole of <sup>12</sup>C atoms is no longer exactly 0.012&nbsp;kg. On the other hand, the dalton ({{aka}} universal atomic mass unit) remains unchanged as {{sfrac|1|12}} of the mass of <sup>12</sup>C.<ref name=pave2018/><ref name=IUPAC/> Thus, the [[molar mass constant]] remains very close to but no longer exactly equal to 1&nbsp;g/mol, although the difference ({{val|4.5|e=-10}} in relative terms, as of March 2019) is insignificant for all practical purposes.<ref name=NIST2019/><ref name=bipm9th/>