How this calculator works
Molecular weight is the older name for relative molecular mass: molecular mass divided by the atomic mass constant. It is dimensionless. For ionic solids, relative formula mass is the corresponding term. Enter symbols with correct capitalization; nested groups and hydrates are expanded by the shared formula parser. No standard atomic weight is assigned to elements without a natural standard value.
Formula
M_r = sum(count_i x A_r,i). Relative mass has no unit; molar mass is approximately the same numerical value in g/mol.
Worked example
Water gives 2 x 1.008 + 15.999 = 18.015. Glucose gives 6 x 12.011 + 12 x 1.008 + 6 x 15.999 = 180.156.
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Frequently asked questions
Is molecular weight measured in grams?
Relative molecular mass has no unit. A molar mass in g/mol is a related quantity.
Can I enter a hydrate?
Yes. For example, CuSO4·5H2O includes five waters per formula unit.
Are isotope labels supported?
No. The parser uses IUPAC 2021 conventional natural-isotope weights, not labelled isotopes.