Find the molar mass of any chemical formula — with parentheses support — or look up a single element's atomic mass.
How to use this tool
Formula mode handles whole compounds; element mode looks up one element's atomic mass.
Use standard symbols with counts after each element: H2O, C6H12O6, Ca(OH)2. Parentheses group parts that repeat.
The headline figure is grams per mole, with the per-element breakdown underneath so you can check the maths.
Divide a sample's mass in grams by the molar mass to get moles — the calculator deliberately does not bundle a separate moles mode, since a dedicated Mole tool covers that job.
Formula & worked example
Water, H2O: 2 × 1.008 + 15.999 = 18.015 g/mol. Calcium hydroxide, Ca(OH)2: 40.078 + 2 × (15.999 + 1.008) = 74.092 g/mol.
Limitations — read this before you rely on it
Atomic weights are standard values and vary slightly by source and by isotopic composition, so results may differ in the third decimal from a textbook that uses different rounding. This calculator covers the most common elements; very rare elements are not in its table and will be rejected rather than guessed. It does not balance equations or check whether a formula is a real stable compound.
Frequently asked questions
The mass of one mole (6.022 × 10²³ particles) of a substance, in grams per mole. It lets you convert between a weighable mass and a countable number of moles.
The number after a closing parenthesis multiplies everything inside it: in Ca(OH)2 the 2 applies to both O and H, giving O₂ and H₂.
Atomic weights are averages over natural isotopes and different tables round differently — 18.015 vs 18.02 for water is the same value at different precision.
No — this calculator finds molar masses only. Balancing equations is a different job with its own rules.
The table covers the elements most students and labs meet. An unknown or mistyped symbol (for example 'FE' instead of 'Fe') is rejected with an error rather than silently guessed.