Molar Mass vs. Molecular Weight
Molar mass (g/mol) is the mass of one mole (6.022 × 10²³) of a substance. It is numerically equal to the molecular weight in atomic mass units (u), but expressed with units g/mol for practical lab calculations.
Molar Mass Calculator
Enter a chemical formula — get the exact molecular weight in g/mol, instantly, in your browser
Zero Upload — calculated entirely in your browser
Try an example:
What Is Molar Mass?
How to Read a Chemical Formula
Subscript numbers after an element symbol (like H₂O) indicate how many atoms of that element are in one molecule. Parentheses (like Ca(OH)₂) group elements — the subscript after the closing bracket multiplies everything inside.
IUPAC Atomic Weights — Our Data Source
Atomic masses in this tool come from the IUPAC 2021 standard atomic weights (Commission on Isotopic Abundances and Atomic Weights). Values are updated as natural isotope abundances are refined.
Stoichiometry in 30 Seconds
Knowing the molar mass lets you convert between grams and moles: moles = mass (g) ÷ molar mass (g/mol). This is the foundation of all reaction stoichiometry calculations.
Frequently Asked Questions
What is the difference between molar mass and molecular weight?
They are numerically the same. Molecular weight is dimensionless (expressed in atomic mass units, u). Molar mass has SI units of g/mol and is used in practical chemistry calculations.
How do I enter a formula with parentheses?
Use standard chemical notation: Ca(OH)2, Al2(SO4)3, Cu(NO3)2. The calculator handles nested parentheses up to 3 levels deep.
Which atomic masses are used?
The tool uses IUPAC 2021 standard atomic weights. For elements with no stable isotopes (like Tc, Po), the mass of the most stable isotope is used, marked with an asterisk.
Can I calculate the molar mass of an ionic compound?
Yes. Enter the formula unit as written: NaCl, CaCO3, Fe2O3. The calculator sums all atomic masses in the formula unit regardless of ionic or covalent bonding.
Atomic masses in this tool come from the IUPAC 2021 standard atomic weights (Commission on Isotopic Abundances and Atomic Weights). Values are updated as natural isotope abundances are refined. IUPAC CIAAW 2021 · NIST Atomic Weights