How this calculator works
Read element symbols with their exact capitalization, expand parentheses or square brackets, and multiply hydrate segments by any leading coefficient. A dot or middle dot separates hydrate components. Unicode subscript digits are accepted. Charges, isotope labels, decimal occupancies and reaction equations are excluded. Formula masses use IUPAC 2021 table 2 conventional single values for natural isotope intervals. Elements without standard weights are rejected. The g/mol value uses the usual chemistry approximation; the CODATA molar mass constant differs at about one part per billion.
Formula
M = sum of atom count x IUPAC 2021 atomic weight, in g/mol. Mean formula-unit mass = relative formula mass x atomic mass constant.
Worked example
H2O gives 2 x 1.008 + 15.999 = 18.015 g/mol. Ca(OH)2 gives 40.078 + 2 x (15.999 + 1.008) = 74.092 g/mol.
Advertisement
Frequently asked questions
Are Co and CO the same?
No. Co is cobalt, while CO contains carbon and oxygen. Capital letters matter.
How do I enter a hydrate?
Use CuSO4·5H2O or CuSO4.5H2O. The 5 multiplies every atom in the water segment.
Why can I not use Tc?
Technetium has no standard atomic weight. Choose an isotope-specific calculation rather than treating a mass number as a natural atomic weight.