Free Molecular Weight Calculator Online

Use this free molecular weight calculator to find the molar mass of any chemical compound. Type a formula like H2O, NaCl, or C6H12O6 and the molecular weight calculator instantly returns the weight in g/mol along with a complete element-by-element breakdown showing each atom count and percent composition.

Examples: H2O, NaCl, C6H12O6, Ca(OH)2, Al2(SO4)3

Molecular Weight

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Enter a chemical formula

How the Molecular Weight Calculator Works

The molecular weight calculator parses your chemical formula character by character, identifying element symbols (one uppercase letter optionally followed by a lowercase letter) and their subscript counts. It then multiplies each element's standard atomic weight by its count and sums the results.

For H2O, the molecular weight calculator identifies H (1.008 g/mol x 2) + O (15.999 g/mol x 1) = 18.015 g/mol. For glucose (C6H12O6), it computes C (12.011 x 6) + H (1.008 x 12) + O (15.999 x 6) = 180.156 g/mol.

The molecular weight calculator also supports parenthetical groups. For Ca(OH)2, it correctly interprets the group: Ca (40.078) + O (15.999 x 2) + H (1.008 x 2) = 74.093 g/mol. This makes it easy to look up complex salts, acids, and coordination compounds.

Common Molecular Weights

H2O (Water)18.015 g/mol
NaCl (Table Salt)58.443 g/mol
C6H12O6 (Glucose)180.156 g/mol
C2H5OH (Ethanol)46.069 g/mol

Verify these with the molecular weight calculator or look up any compound.

Why Molecular Weight Matters

Solution Prep

To prepare a 1M solution, you need one mole (molecular weight in grams) per liter. The molecular weight calculator tells you exactly how many grams to weigh out.

Stoichiometry

Converting between grams and moles requires molecular weight. Reaction calculations depend on molar ratios, making the molecular weight calculator essential for chemistry.

Analysis

Percent composition from the molecular weight calculator helps identify unknown compounds and verify purity through elemental analysis.

Frequently Asked Questions

Disclaimer: This molecular weight calculator uses standard IUPAC atomic weights. For isotope-specific calculations, use the exact isotopic mass instead.

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