Molecular Weight (Molar Mass) Calculator
Compute molar mass from a chemical formula, including parentheses and multipliers. You’ll get a total molar mass in g/mol plus a per-element breakdown and percent composition. Everything runs locally in your browser.
Formula
Supports parentheses and multipliers like Ca(OH)2 and Al2(SO4)3.
Saved locally in your browser.
Molar mass snapshot
Molecular Weight (Molar Mass)
Formula: Ca(OH)2
| Element | Count | Atomic mass | Contribution | % |
|---|---|---|---|---|
CaCalcium | 1 | 40.078 | 40.078 | 54.09 |
OOxygen | 2 | 15.999 | 31.998 | 43.19 |
HHydrogen | 2 | 1.008 | 2.016 | 2.72 |
| Total | 74.092 | 100.00 |
Mass contribution (percent)
Atomic masses are standard average atomic weights. This calculator is educational and may differ slightly from specific lab references.
What is molar mass?
Molar mass (sometimes called molecular weight) is the mass of one mole of a substance. For a pure chemical compound, the molar mass is found by adding the atomic masses of each element in the formula, multiplied by how many atoms of that element appear in the compound. The usual unit is grams per mole (g/mol).
How to read chemical formulas with parentheses
Parentheses group atoms together so a multiplier applies to everything inside the group. For example, in Ca(OH)2, the 2 applies to both O and H, meaning the formula contains 1 Ca, 2 O, and 2 H. In Al2(SO4)3, the 3 applies to S and O4, so you have 2 Al, 3 S, and 12 O.
Percent composition
Percent composition tells you what fraction of the total molar mass comes from each element. This is useful for chemistry homework, preparing lab solutions, and checking whether an experimental measurement is consistent with a proposed formula.
Notes about accuracy and references
Atomic masses are standard average atomic weights. Different references may round values differently or use isotopic masses for specialized problems, so small differences are expected depending on context. Use the breakdown table to see exactly which atomic masses were used in the calculation.
This molar mass calculator runs entirely in your browser and does not upload your formulas to a server. It stores your last-used formula in localStorage for convenience (clearing your browser data removes that history).