Sulfuric acid H2SO4
Multiply each element's atomic weight by its number of atoms, then add the products.
- H 2 × 1.008 = 2.016
- S 1 × 32.06 = 32.06
- O 4 × 15.999 = 63.996
M(H2SO4) = 98.072 g/mol ≈ 98.07 g/mol
Open this example in the toolTool 01
Molar mass calculator
Type a chemical formula, an ion or a common substance name to get its molar mass in grams per mole and the mass percentage of each element. Brackets, hydrates, charges and lower-case input are all understood.
Free, no account, and nothing you type leaves your browser.
Molar mass & percentage composition
Nested brackets, hydrate dots and ionic charges all parse. Try Ca(OH)2, CuSO4·5H2O or Fe2(SO4)3.
Worked examples
Calcium hydroxide Ca(OH)2
The 2 after the bracket doubles everything inside it: two oxygen and two hydrogen atoms.
- Ca 1 × 40.078 = 40.078
- O 2 × 15.999 = 31.998
- H 2 × 1.008 = 2.016
M(Ca(OH)2) = 74.092 g/mol ≈ 74.09 g/mol
Open this example in the toolBlue vitriol CuSO4·5H2O
A hydrate counts its water too: five H₂O add 10 hydrogen and 5 oxygen atoms to CuSO₄.
- Cu 1 × 63.546 = 63.546
- S 1 × 32.06 = 32.06
- O 9 × 15.999 = 143.991
- H 10 × 1.008 = 10.08
M(CuSO4·5H2O) = 249.677 g/mol ≈ 249.68 g/mol
Open this example in the toolHow it works
How is molar mass calculated?
Every element in the formula contributes its standard atomic weight multiplied by how many atoms of it appear. Those weights are averages across each element's natural isotope mix, which is why they are rarely whole numbers — chlorine is 35.45 because roughly three quarters of natural chlorine is Cl-35 and one quarter Cl-37. Percentage composition is each element's total contribution divided by the whole.
What you can type
Type formulas as you would write them by hand. Brackets can nest, a dot or · joins the parts of a hydrate (CuSO4·5H2O), and a number at the start multiplies the whole formula (2H2O). Lower-case input such as nacl is read with valid element symbols, and when there are two readings, as with co (CO or Co), both are shown. About 70 common substance names, such as table salt or baking soda, work in every language of the site.
Hydrate coefficients can be decimals or fractions, so CaSO4·0.5H2O, CaSO4·0,5H2O and CaSO4·1/2H2O all work. An entry can be up to 200 characters long.
How charges are read
A charge can follow a caret (SO4^2-), be written in superscript (SO₄²⁻), follow a bracket ([SO4]2-) or come straight after the formula. A bare charge is read the way chemists write it: with two digits before the sign, the last one is the charge (SO42- is sulfate, 2−); a single element followed by a digit and a sign is an ion with that charge (Fe3+); otherwise the digit belongs to the formula (NH4+ is ammonium, 1+). The result always shows how the input was read.
A sign written before the number gives the same charge: Fe+3 is Fe³⁺ and SO4-2 is SO₄²⁻. A subscript of 1 is never written, so in C6H12+ the 12 stays a subscript and the charge is 1+. A positive charge larger than the number of electrons the atoms have is reported as an error.
Limits
- It uses standard atomic weights, the averages over each element's natural isotopes, so it does not give the mass of a single isotope or of an isotopically labelled compound.
- Some standard atomic weights, such as those of lithium, boron and sulfur, vary between natural samples, so the last digits shown are not significant for every source.
- The electrons an ion gains or loses are not counted; each would change the mass by about 0.00055 g/mol.
- It knows about 70 substance names. For anything else, type the formula.
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