How this molar mass calculator works
The molar mass of a substance is the mass of one mole of it, measured in grams per mole (g/mol). Because a mole always contains the same number of particles, the molar mass is simply the sum of the standard atomic weights of every atom written in the chemical formula. That same number is what chemists call the molecular weight or formula weight.
This tool reads your formula left to right. Each element symbol (one capital letter, optionally followed by lowercase letters) may be followed by a subscript count. A group in parentheses applies its trailing number to every atom inside, and groups can be nested. A centre dot (· or .) marks a hydrate, so the number before a fragment like 5H2O multiplies that whole fragment. The calculator then multiplies each element's atomic weight by its total count and adds the contributions.
Reference note: atomic masses use IUPAC standard atomic weights (conventional values), which represent natural isotopic abundance. Results are accurate to a few decimal places and are intended for education, not for analytical or regulatory work.
Frequently asked questions
- What is molar mass?
- Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). Numerically it equals the sum of the standard atomic weights of all the atoms in the chemical formula, so it is the molecular or formula weight of the substance.
- How is molar mass calculated?
- Multiply the standard atomic weight of each element by the number of atoms of that element in the formula, then add all the contributions. For water, H2O, that is 2 × 1.008 for hydrogen plus 1 × 15.999 for oxygen, giving about 18.02 g/mol.
- What is the difference between molar mass and molecular weight?
- They are numerically the same value. Molecular weight (or formula weight) is a relative, dimensionless number, while molar mass carries the unit grams per mole (g/mol). For everyday calculations you can treat them as identical.
- How do I enter a formula with parentheses?
- Write the group in parentheses followed by its multiplier, like Ca(OH)2 or Al2(SO4)3. The number after the closing parenthesis multiplies every atom inside the group. You can also nest groups and use a centre dot for hydrates, for example CuSO4·5H2O.
- What units does molar mass use?
- Molar mass is reported in grams per mole (g/mol). Atomic masses come from the IUPAC standard atomic weights, expressed in unified atomic mass units (u), and a value in u is numerically equal to the molar mass in g/mol.
- How do I find the mass percent of an element?
- Divide the total mass contributed by that element by the molar mass of the whole compound, then multiply by 100. This calculator shows the mass percent for every element automatically in the breakdown table.