Molecular Mass Calculator
Calculate the molecular mass (relative molecular mass, Mr) of any compound from its chemical formula. Enter a formula to get the molecular mass in Daltons with a complete element breakdown, percentage composition, and export options. Uses IUPAC 2021 standard atomic weights for all 118 elements.
Ingrese una fórmula química arriba para calcular el peso molecular
Real-Time Molecular Mass Computation
See the molecular mass update character by character as you type your formula.
The molecular mass calculator parses your chemical formula in real time using a recursive descent parser. Each element symbol is identified, nested groups within parentheses and brackets are resolved, and atom counts are determined accurately.
The relative molecular mass (Mr) is computed by summing the products of each element's relative atomic mass (Ar) and its atom count. The result equals the mass of one molecule in Daltons (Da) and is numerically identical to the molar mass in g/mol.
This approach matches the methodology used by PubChem, the NIST Chemistry WebBook, and analytical chemistry reference databases for molecular mass determination.
Relative Atomic Masses Used in Calculation
Molecular mass depends on accurate relative atomic masses for each element.
Every molecular mass calculation starts with the relative atomic mass (Ar) of each element. These values represent weighted averages of naturally occurring isotopes — for Silicon, 28.085 reflects the mix of ²⁸Si (92.2%), ²⁹Si (4.7%), and ³⁰Si (3.1%).
The IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) publishes updated Ar values periodically. This calculator uses the 2021 standard, matching values in the CRC Handbook of Chemistry and Physics.
For transition metals and post-transition metals, the relative atomic masses can be significantly higher — Tungsten at 183.84 and Platinum at 195.08. Explore the element cards below to see atomic masses used in molecular mass calculations.
How to Calculate Molecular Mass
Three steps to find the molecular mass of any chemical compound.
Enter the Molecular Formula
Type the chemical formula of your compound using standard notation. The molecular mass calculator recognizes all 118 elements, parentheses for polyatomic groups like (SO₄), and nested brackets for coordination compounds. Case sensitivity matters — Co is Cobalt while CO is Carbon Monoxide.
Molecular Mass Examples
Click any compound to load it and see its molecular mass breakdown.
Molecular Mass FAQ
Answers to common questions about molecular mass, relative atomic mass, and this calculator.