Molar Mass Calculator
Find the molar mass of any chemical formula, with each element's count, mass and percent composition. Handles brackets such as Ca(OH)2 and Fe2(SO4)3.
What this calculator does
Type a chemical formula and get its molar mass in g/mol, a table with the count, atomic mass and subtotal of every element, and the percent composition by mass.
When you need it
Nearly every chemistry calculation starts here: converting grams to moles for stoichiometry, preparing solutions in the lab, and finding percent composition for empirical formulas. General chemistry courses and exams ask for molar masses constantly.
Formulas
- M = Σ (number of atoms of each element × its atomic mass)
- mass percent of an element = (mass of that element in one mole ÷ molar mass) × 100
How to use it
- Type the formula using capital letters for elements and numbers for subscripts, for example H2SO4.
- Use brackets for groups, for example Ca(OH)2 or Fe2(SO4)3.
- Press Enter or the calculate button to see the molar mass and the breakdown by element.
Worked example
Find the molar mass of sulfuric acid, H2SO4.
- H: 2 × 1.008 = 2.016 g/mol
- S: 1 × 32.06 = 32.06 g/mol
- O: 4 × 16.00 = 64.00 g/mol
- Add them: 2.016 + 32.06 + 64.00 = 98.076 g/mol
Answer
The molar mass of H2SO4 is about 98.08 g/mol.
Common mistakes
- Forgetting to multiply the atoms inside brackets: in Ca(OH)2 there are 2 O and 2 H, not 1.
- Writing a lowercase letter for an element (co is not CO, it is not an element symbol).
- Mixing up molar mass (g/mol) with the mass of one molecule.
Related tools
- Stoichiometry calculator
- Limiting reagent calculator
- Concentration calculator
- Interactive periodic table
Frequently asked questions
What is molar mass?
Molar mass is the mass of one mole of a substance, in grams per mole. For a compound it is the sum of the atomic masses of all the atoms in its formula.
How do I calculate the molar mass of Ca(OH)2?
Multiply what is inside the brackets by the subscript outside: Ca is 40.08, two O are 32.00 and two H are 2.016, so the total is 74.10 g/mol.
Is molar mass the same as molecular weight?
They have the same number. Molar mass is written in g/mol, while molecular weight is the same quantity without that unit.