Molar Mass Calculator
The molar mass of any chemical formula, with brackets and hydrates, its mass percent by element, and grams to moles both ways.
Result…
How it's calculated
Molar mass = Σ (count of each element × its standard atomic weight) Moles = mass ÷ molar mass Mass = moles × molar mass Mass % of an element = its share ÷ molar mass × 100
Each element adds its standard atomic weight (in g/mol) once for every atom in the formula. Brackets multiply everything inside them, and the part after a dot in a hydrate counts as many times as the number in front of it, so CuSO4·5H2O adds five waters. Atomic weights are the Commission on Isotopic Abundances and Atomic Weights (CIAAW) abridged values. Elements with no stable isotopes, such as technetium and radon, have no standard atomic weight and are refused.
Your numbers, step by step
About the Molar Mass calculator
This molar mass calculator reads a chemical formula, adds up the standard atomic weight of every atom in it and gives the molar mass in g/mol. It handles nested brackets such as Ca3(PO4)2 and K4[Fe(CN)6], and hydrates written with a dot, such as CuSO4·5H2O. Beside the answer it lists each element's share of the mass as a percentage, and it can turn a mass in grams, milligrams, kilograms, ounces or pounds into moles, or moles back into mass. Chemistry students use it for stoichiometry homework, and lab staff use it when weighing out a reagent. The atomic weights are the abridged standard values published by the IUPAC Commission on Isotopic Abundances and Atomic Weights. The steps show every element's count times its weight, so you can check each line.
How to use it
- Type the formula into “Chemical formula”, with capital letters where the symbols have them (Co is cobalt, CO is carbon monoxide).
- For a hydrate, put a dot or a · before the water, as in CuSO4·5H2O.
- Under “Also convert”, choose “Mass → moles” or “Moles → mass”, or “Nothing” for the molar mass alone.
- Enter the “Mass” or the “Amount” in mol, and pick the “Mass unit”.
- Read the molar mass, the conversion and the mass percent of each element.
Worked example
Calcium hydroxide, Ca(OH)2, has one calcium, two oxygens and two hydrogens: 40.078 + 2 × 15.999 + 2 × 1.0080 = 74.092 g/mol. Calcium is 54.09% of the mass and oxygen 43.19%. So 10 g of it is 10 ÷ 74.092 = 0.13497 mol, about 8.128 × 10^22 formula units.
Updated
Questions people ask
How do I calculate the molar mass of a compound?
Multiply each element's atomic weight by the number of its atoms in the formula, then add the results. Brackets multiply everything inside them by the number after them.
How do I convert grams to moles?
Divide the mass in grams by the molar mass in g/mol. To go back, multiply the moles by the molar mass. The mole fraction calculator then compares moles across a mixture.
How do I enter a hydrate like copper sulfate pentahydrate?
Write the salt, a dot and the waters with their number in front: CuSO4·5H2O or CuSO4.5H2O. The calculator adds five H2O, giving 249.677 g/mol.
Why is my answer slightly different from my textbook?
Books round atomic weights differently, for example 35.5 or 35.453 for chlorine instead of 35.45. Differences in the second decimal place usually come from that, not from a mistake.
Why can't it find radon or technetium?
Those elements have no stable isotopes, so there is no standard atomic weight. Their mass depends on the isotope, which you would need to look up and add yourself.