Molar Mass Calculator with Mass Percent

Every stoichiometry problem starts by turning a formula into grams per mole. Type the formula here and the Molar Mass Calculator adds up the atomic weights, breaks the total into each element’s share, and converts a mass you have into moles and particles.

It reads formulas as chemists write them. Three kinds of bracket can nest, a hydrate can follow a dot, and subscripts pasted from a document (H₂O) are understood. It also gives the Hill formula, which is the order a chemical database would index the compound under.

Worked Example: 25 Grams of Glucose

The tool opens on C6H12O6 with 25 g in the mass box. The result:

• Molar mass: 180.156 g/mol, from 6 × 12.011 + 12 × 1.008 + 6 × 15.999
• Mass percent: carbon 40.00%, hydrogen 6.71%, oxygen 53.28%
• Amount: 25 ÷ 180.156 = 0.138769 mol
• Particles: 8.3568 × 10²² molecules

Flip I have to moles and the same box takes an amount instead, returning grams. The next sample is CuSO4·5H2O at 0.05 mol, which comes to 249.677 g/mol and 12.484 g.

Input Format: Brackets, Hydrates and Charges

• Groups in ( ), [ ] or { }, nested: K4[Fe(CN)6] is 368.345 g/mol
• Hydrates joined by ·, * or a full stop, with a leading coefficient that may be a decimal, as in CaSO4·0.5H2O
• A charge at the end after a caret, SO4^2-, which is noted and ignored

Case is significant, since Co is cobalt and CO is carbon monoxide. A symbol that does not exist is caught by position: “"Xy" at position 1 is not an element symbol.” Subscripts must be whole numbers, and a count of 0 is refused rather than silently dropping the atom.

Precision of the Atomic Weights Used

The table holds the IUPAC abridged standard atomic weights for all 118 elements. Those are the values printed on most classroom periodic tables, so hydrogen is 1.008 and chlorine 35.45, and results are shown to three decimal places. Textbooks that use 1.00794 for hydrogen will differ in the third decimal. For elements with no stable isotope, such as technetium, the mass number of the longest-lived isotope appears in brackets, [98].