Science / Chemistry
Molar Mass Calculator
Find the molar mass of any chemical formula, with brackets and hydrates such as CuSO4·5H2O, each element's share by mass, and grams-to-moles conversion.
Molar Mass Calculator: The formula is read into a count of each element's atoms, including groups in brackets multiplied by their subscript and waters of crystallisation after a dot. Each count is multiplied by the element's standard atomic weight from IUPAC, and the products are added up. The mass percentage of each element is its share of the total. Moles are grams divided by molar mass, and the number of molecules is moles times the Avogadro constant, 6.022 140 76 × 10²³ per mole. Runs 100% locally in your browser with zero server file uploads.
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C₆H₁₂O₆: 180.156 g/mol
| Element | Atoms | Atomic weight | Mass | Share by mass |
|---|---|---|---|---|
| C | 6 | 12.011 | 72.066 | 40% |
| H | 12 | 1.008 | 12.096 | 6.71% |
| O | 6 | 15.999 | 95.994 | 53.28% |
Atomic weights are IUPAC standard atomic weights. Brackets, square brackets, and hydrates such as CuSO4·5H2O are understood; charges are ignored.
From formula to grams
Molar mass links what you weigh to how many particles react. Once a reaction is balanced with the chemical equation balancer, the coefficients give the moles that react, and the molar mass turns them into grams: in 2H₂ + O₂ → 2H₂O, 4.03 g of hydrogen reacts with 32.00 g of oxygen.
For the arithmetic of concentrations and dilutions, the scientific calculator handles powers of ten and logarithms.
Mass percentage
The share of each element by mass, also called percent composition, is useful for fertiliser labels, nutrition, and checking an analysis: water is 88.8% oxygen by mass even though only one of its three atoms is oxygen.
How to use it
- Type a formula, such as H2SO4, Ca(OH)2, or CuSO4·5H2O.
- Read the molar mass and the table of atoms, masses, and percentages.
- Enter grams to get moles and the number of molecules, or moles to get grams.
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Frequently asked questions
What is molar mass?
The mass of one mole of a substance, in grams per mole. One mole is 6.022 × 10²³ particles, chosen so that the molar mass in g/mol equals the relative molecular mass: water, H₂O, is 2 × 1.008 + 15.999 = 18.015 g/mol.
How do I write a hydrate?
Put a dot, or an asterisk, before the water: CuSO4·5H2O or CuSO4*5H2O. The number before H2O multiplies the whole water molecule.
Why do different sources give slightly different values?
Atomic weights are revised by IUPAC as measurements improve, and some elements, such as hydrogen, carbon, and oxygen, vary a little in nature, so tables round them differently. The differences are usually in the second or third decimal place.
How do I convert grams to moles?
Divide the mass by the molar mass: 36 g of water is 36 ÷ 18.015 = 2.0 mol. To go the other way, multiply moles by the molar mass.
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