Molar Mass Calculator
Type a formula such as H2O, Ca(OH)2 or CuSO4.5H2O. You get the molar mass and the share of each element.
Use capital letters to start each element: Co is cobalt but CO is carbon monoxide. Brackets multiply what is inside. Join hydrates with a dot, as in CuSO4.5H2O.
Worked examples
Calcium hydroxide
Ca(OH)2
74.092 g/mol
40.078 + 2 x 17.007.
Hydrated copper sulfate
CuSO4.5H2O
249.677 g/mol
159.602 for CuSO4 plus 5 x 18.015.
About Molar Mass Calculator
The molar mass of a substance is the mass in grams of one mole of it, which is 6.02214076 times ten to the twenty-third particles. It is found by adding up the standard atomic weights of every atom in the formula. Water, H2O, has two hydrogens at 1.008 and one oxygen at 15.999, giving 18.015 grams per mole. Molar mass is the bridge between a mass you weigh in the lab and a number of moles in a reaction.
This calculator reads formulas with brackets, nested brackets and hydrates, so Al2(SO4)3, K4[Fe(CN)6] and CuSO4.5H2O all work. A table breaks the answer into each element, showing the atomic weight used, the mass it contributes and its mass percent in the compound. The atomic weights are the IUPAC standard values in the abridged table. For radioactive elements with no stable isotopes, the mass number of the longest-lived isotope is used, and the page says so.
How to use Molar Mass Calculator
- Type the formula, using a capital letter to start each element symbol.
- Use brackets for groups, such as Ca(OH)2, and a dot before a number for water of crystallisation.
- Read the molar mass in grams per mole.
- Use the table for the mass of each element and its mass percent.
Common uses
- Preparing solutions by weighing out the right mass
- Converting between grams and moles in stoichiometry
- Finding the percentage composition of a compound
- Checking homework on molecular and formula masses
Frequently asked questions
How do I calculate molar mass?
Multiply the atomic weight of each element by the number of its atoms in the formula and add the results. For Ca(OH)2 that is 40.078 + 2 x (15.999 + 1.008) = 74.092 grams per mole.
Why does case matter in a formula?
A capital letter starts each element and a small letter continues it. Co is cobalt but CO is carbon and oxygen, so typing the wrong case changes the answer.
How do I enter a hydrate?
Join the parts with a dot or a middle dot and put the number of water molecules in front, as in CuSO4.5H2O. The page adds five waters to the copper sulfate.
Where do the atomic weights come from?
They are the conventional standard atomic weights from the International Union of Pure and Applied Chemistry, abridged to the precision normally used in teaching and labs.