Frequently Asked Questions
Common questions about the free molar mass calculator — how it works, complex formulas, percent composition, mass-to-moles conversion, accuracy, and privacy.
How does the molar mass calculator work?
Type a chemical formula and the tool parses each element symbol and its subscript count, multiplies each by its standard atomic weight, and sums the results to give the total molar mass in g/mol — updating instantly as you type, no button refresh needed.
Is this molar mass calculator free to use?
Yes, it's completely free with no sign-up, downloads, or limits. Calculate as many formulas as you need, as often as you like. Everything runs in your browser and your data is never sent to a server.
What is molar mass?
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It equals the sum of the atomic weights of all atoms in the chemical formula. For water (H₂O), that is 2 × 1.008 + 15.999 = 18.015 g/mol. Molar mass lets you convert between a measurable mass in grams and the number of moles you have, which is central to all stoichiometry calculations.
Can it handle parentheses and complex formulas?
Yes. The parser uses a stack-based algorithm that handles nested parentheses and subscript multipliers correctly. For example, Ca(OH)₂ expands to Ca, 2×O, 2×H, and Al₂(SO₄)₃ expands to 2×Al, 3×S, 12×O. Any depth of nesting is supported.
Does it support hydrates like CuSO₄·5H₂O?
Yes. The calculator recognises the hydrate dot notation, accepting both the middle dot (·) and a plain period (.) as separators. The number after the dot multiplies the formula that follows, so CuSO₄·5H₂O correctly adds 5 water molecules (10×H, 5×O) to the copper sulfate, giving a molar mass of approximately 249.68 g/mol.
Does it show percent composition?
Yes. Along with the total molar mass, the per-element breakdown table shows each element's contribution in g/mol and its percentage by mass. A proportional bar in the table makes it easy to compare contributions at a glance. The percentages sum to 100%.
Can it convert between grams and moles?
Yes. The Mass ↔ Moles conversion panel lets you enter a mass in grams to get the number of moles (moles = mass ÷ molar mass), or enter a number of moles to get the mass in grams (mass = moles × molar mass). Both fields update instantly, and when you change the formula the conversion recalculates automatically.
How accurate are the atomic weights used?
The calculator uses standard IUPAC atomic weights, the same values used in chemistry textbooks and coursework. For example, H = 1.008, C = 12.011, O = 15.999, Na = 22.990, Cl = 35.453. Results are displayed to four decimal places, which is consistent with the precision of the underlying atomic weight data.
Does it work on mobile devices?
Yes, the tool is fully responsive and works on smartphones, tablets, and desktops without any installation. The formula input, results table, percent-composition bars, and mass-to-moles conversion all adapt to the screen width.
What if I enter an invalid formula?
If a formula can't be parsed — for example an unknown element symbol like Xy, a lowercase start like h2o instead of H2O, or mismatched parentheses — the tool shows a specific error message describing the problem so you can correct it. It will not return a wrong result for an invalid formula.