Molecular Weight Calculator
Calculate the molecular weight of any chemical compound by entering its formula. This molecular weight calculator uses IUPAC 2021 standard atomic weights to compute the molar mass in g/mol with a full element breakdown, percentage composition bars, and export options. Supports all 118 elements, parentheses, brackets, and nested formula groups.
Enter a chemical formula above to calculate molecular weight
Instant Molecular Weight Calculation
Watch the molecular weight appear as you type — no button clicks, no page reloads.
This molecular weight calculator processes each character in real time through a recursive descent chemical formula parser. The engine identifies element symbols, resolves parentheses and bracket groups, and multiplies each element's count by its IUPAC standard atomic weight.
Three outputs update with every keystroke: total molecular weight in g/mol, a per-element mass breakdown table, and percentage composition bars for elemental analysis. These values match data from PubChem, ChemSpider, and Sigma-Aldrich catalogs.
For laboratory and research use, the calculator provides values suitable for stoichiometric calculations, mass spectrometry isotopic distribution analysis, and reagent preparation worksheets.
Atomic Weights from the Periodic Table
Every molecular weight calculation starts with accurate atomic masses from the IUPAC standard.
The molecular weight of any compound depends on the standard atomic weights of its constituent elements. This calculator uses the IUPAC 2021 standard atomic weights — the same reference data used by PubChem, the NIST Chemistry WebBook, and professional chemistry software.
Each atomic weight reflects the natural isotopic distribution on Earth. For example, Carbon's atomic weight of 12.011 g/mol accounts for the natural mix of ¹²C (98.9%) and ¹³C (1.1%). These weighted averages ensure the molecular weight output matches real-world measurements.
The element database covers all 118 elements from Hydrogen (Z=1, 1.008 g/mol) to Oganesson (Z=118). Hover over the element cards below to explore atomic weights used in molecular weight calculations.
How to Calculate Molecular Weight
Follow 3 simple steps to find the molecular weight of any compound.
Type a Chemical Formula
Enter your molecular formula using standard notation — capitalize the first letter of each element symbol, use lowercase for the second letter, and type subscript numbers directly. The parser handles parentheses, brackets, and braces for nested groups like Ca(OH)₂ or K₄[Fe(CN)₆]₃. All 118 elements from Hydrogen (H) to Oganesson (Og) are recognized.
Molecular Weight Examples
Click any molecule to load it into the calculator and see the full element breakdown.
Molecular Weight Calculator FAQ
Common questions about molecular weight calculation, formulas, atomic weights, and export options.