Molar Mass Calculator
Case matters (Co is cobalt, CO is carbon monoxide). Parentheses, brackets and hydrates (CuSO4·5H2O or CuSO4*5H2O) work.
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Molar mass
Ca(OH)₂: 74.092 g/mol
5 atoms per formula unit. One mole weighs 74.092 g and contains 6.022 × 10²³ formula units.
Composition by mass
| Element | Atoms | Atomic mass | Mass (g/mol) | Mass % |
|---|---|---|---|---|
| Ca Calcium | 1 | 40.078 | 40.078 | 54.09% |
| O Oxygen | 2 | 15.999 | 31.998 | 43.19% |
| H Hydrogen | 2 | 1.008 | 2.016 | 2.72% |
Grams to moles
10 g ÷ 74.092 g/mol = 0.13497 mol = 8.128 × 10²² formula units
Calculate the molar mass of any chemical formula, including parentheses, brackets and hydrates, with the mass percent of each element and a grams-to-moles conversion, from IUPAC standard atomic weights.
Formula
Worked Example
One calcium (40.078), two oxygens (2 × 15.999) and two hydrogens (2 × 1.008) add up to 74.092 g/mol. A 10 g sample is therefore 10 ÷ 74.092 = 0.135 mol, or 8.13 × 10²² formula units.
Frequently Asked Questions
How do I calculate molar mass?
Multiply each element's atomic mass from the periodic table by the number of its atoms in the formula and add them. For water, H₂O: 2 × 1.008 + 15.999 = 18.015 g/mol. Atoms inside parentheses are multiplied by the subscript after them.
What is the difference between molar mass and molecular weight?
Numerically they are the same. Molar mass is the mass of one mole in grams per mole (g/mol); molecular weight is the mass of one molecule relative to 1/12 of a carbon-12 atom and has no unit, or is given in daltons.
How are hydrates handled?
The water molecules count as part of the formula. CuSO₄·5H₂O has a molar mass of 159.60 + 5 × 18.015 = 249.68 g/mol, which matters when weighing out the blue crystals rather than the anhydrous powder.