Molar Mass Calculator
Type any chemical formula and get its molar mass in g/mol, the percent of each element, every step of the math, and a grams-to-moles converter.
Chemistry teachers want the work, not just the number. This calculator reads the formula the way you would on paper — parentheses, brackets and hydrates like CuSO4·5H2O included — then lays out each element's atoms × atomic mass so you can check your own setup line by line. Atomic masses are the standard values printed on most periodic tables.
Element by element
Atoms in one formula unit × atomic mass = that element's share of the molar mass.
| Element | Atoms | Atomic mass | Mass (g/mol) | Mass % |
|---|---|---|---|---|
| Molar mass | 100% | |||
Percent composition
Share of the total mass that comes from each element.
Show your work
Copy this setup onto your homework.
Grams, moles & particles
Enter any one amount — the other two fill in using this molar mass and Avogadro's number (6.02214076 × 1023).
How to type formulas (and common mistakes)
- Capital letters matter. Every element symbol starts with a capital:
Cois cobalt, butCOis carbon monoxide. TypeNaCl, notnacl. - Numbers after a symbol are subscripts.
H2Omeans two hydrogens and one oxygen. - A number after parentheses multiplies everything inside.
Ca(OH)2has 2 oxygens and 2 hydrogens. Square brackets work the same way. - Hydrates: use a dot,
*, or.—CuSO4·5H2O,CuSO4*5H2OandCuSO4.5H2Oall work. The 5 multiplies the whole water molecule. - Ions: write the charge after a caret, like
SO4^2-. Electrons weigh so little that the charge does not change the answer at this precision. - Why your textbook might differ by 0.01: some books round atomic masses first (H = 1, O = 16). Round the same way your teacher does. Elements with no stable isotopes (like radon) use the mass number of their longest-lived isotope, shown in brackets.
Everything runs in your browser. Your last formula is remembered on this device only.