Molecular Weight Calculator
Calculate molecular or formula weight from a chemical formula, including parentheses and hydrate-dot notation for common elements.
Calculate molecular weight from a chemical formula
Parse a chemical formula with element symbols, parentheses and hydrate dots to estimate average molar mass.
How the Molecular Weight Calculator works
Molecular/formula weight is the sum of each element’s average atomic weight multiplied by the number of atoms in the chemical formula. The parser reads normal element symbols and integer subscripts, supports grouped parentheses, and treats a dot-separated leading coefficient as a hydrate/solvate multiplier.
How to use this molecular weight calculator
Type a formula such as C6H12O6, Ca(OH)2 or CuSO4.5H2O. Capitalization matters because element symbols are case-sensitive. The tool reports grams per mole using average atomic weights stored in the page, along with the atom and distinct-element counts as quick checks on parsing.
How to interpret the result
For compounds that exist as salts or hydrates, the exact form matters. An anhydrous reagent and a pentahydrate have different formula weights, which affects molarity and mass calculations. Use the formula printed on the reagent label or certificate rather than assuming the common form.
Assumptions and limitations
Average atomic weights are not exact isotope masses. The tool does not parse isotope labels such as 13C or deuterium notation, formal charges, polymers with variable n, or non-stoichiometric materials. For high-precision mass spectrometry, use monoisotopic/exact-mass data and isotope-specific software.
Practical example and workflow
CuSO4.5H2O is parsed as one copper, one sulfur, nine oxygens and ten hydrogens after adding five waters of hydration. The resulting formula weight is substantially higher than anhydrous CuSO4, demonstrating why hydrate notation cannot be ignored when preparing molar solutions.