Chemistry Tools
Enter a chemical formula and instantly calculate the molar mass. Supports parentheses and all common elements.
Molar Mass
18.015 g/mol
Use element symbols with optional counts (e.g. H2O means 2 hydrogen, 1 oxygen). Parentheses with multipliers are supported: Ca(OH)2 means 1 calcium, 2 oxygen, 2 hydrogen. Unknown elements will show an error.
Molecular weight, also called molar mass, is the sum of atomic weights of all atoms in a molecule, measured in grams per mole (g/mol). For example, water (H₂O) has a molar mass of 18.015 g/mol: hydrogen (1.008 × 2) plus oxygen (15.999). Understanding molecular weight is essential for stoichiometry, chemical reactions, and lab calculations.
Enter a chemical formula using element symbols and numbers. The calculator instantly displays the total molar mass, shows a detailed element breakdown with individual contributions, and flags any unknown elements. Supports parentheses with multipliers like Ca(OH)₂.
Molar Mass = Σ (Atomic Weight × Count) for each element. For Ca(OH)₂: (40.078 × 1) + (15.999 × 2) + (1.008 × 2) = 74.093 g/mol.Molar mass is the weighted sum of each element's atomic weight multiplied by how many atoms of that element are present. For molecules with parentheses, expand first: Ca(OH)₂ means 1 Ca, 2 O, and 2 H. The calculator handles this parsing automatically.
| Input | Result | Notes |
|---|---|---|
| H2O | 18.015 g/mol; H: 2.016, O: 15.999 | Water: 2 hydrogen (1.008 each) + 1 oxygen (15.999) |
| C6H12O6 | 180.156 g/mol; C: 72.066, H: 12.096, O: 95.994 | Glucose: 6 carbon + 12 hydrogen + 6 oxygen |
| Ca(OH)2 | 74.093 g/mol; Ca: 40.078, O: 31.998, H: 2.016 | Calcium hydroxide: 1 Ca + (2 OH groups) = 1 Ca + 2 O + 2 H |
Molecular weight and molar mass are numerically identical but conceptually different. Molecular weight is the mass of one molecule in atomic mass units (amu). Molar mass is the mass of one mole (6.022 × 10²³ molecules) in grams per mole (g/mol). In practice, they describe the same values.
Check that element symbols are capitalized correctly (H for hydrogen, not h), and that counts are plain numbers directly after the element (H2O, not H 2 O). Parentheses must match: Ca(OH)2 is correct, but Ca(OH2 is not.
Enter the main compound and water separately: find CuSO4 (159.609 g/mol) and 5×H2O (5 × 18.015 = 90.075 g/mol), then add them (249.684 g/mol). Or search for the full formula in a reference table.
Most organic molecules do not nest parentheses deeply. If a formula has complex nesting like Ca((OH)2)3, expand from the inside out carefully, or break it into sub-components and add the totals.
No. This calculator uses standard atomic weights (average across natural isotopes). For specific isotopes, consult isotope tables or a specialized physics calculator.
Atomic weights vary slightly between sources (rounding and precision differ). This calculator uses IUPAC standard atomic weights. Small differences (less than 0.05 g/mol) are normal.