The relative atomic weight (atomic mass) of sulfur has both a commonly used approximate value and a precise standard value defined by IUPAC:
Common Approximate Value
For general chemical calculations, industrial formula calculations and routine technical scenarios, sulfur’s atomic weight is typically rounded to 32.
Standard Precise Value
According to the IUPAC 2021 standard, the standard atomic weight of sulfur is given as the interval [32.059, 32.076], due to natural variations in the isotopic composition of sulfur from different geological sources. For most laboratory and engineering applications, the fixed value 32.06 g/mol is universally adopted.
Isotopic Background
This weighted average comes from sulfur’s four stable naturally occurring isotopes:
- ³²S: mass number 32, ~95.02% natural abundance (the overwhelmingly dominant isotope)
- ³³S: ~0.75% abundance
- ³⁴S: ~4.21% abundance
- ³⁶S: ~0.02% abundance
Related Note
Consistent with the S₈ crown-ring molecular structure of standard sulfur powder, the molar mass of the S₈ molecule is approximately 8 × 32.06 = 256.48 g/mol.
