Last updated October 10, 2026 · Report an error
A compound's molecular weight is the sum of the atomic weights of every atom in its formula.
This calculator parses a chemical formula — including nested parentheses like Ca(OH)2 — and computes its total molecular weight from standard atomic weights.
How it works
Enter a chemical formula using standard element symbols and subscript numbers (e.g. C6H12O6). The calculator parses the formula, including any parenthesized groups with their own multipliers, and sums each element's atomic weight times its count.
- Enter chemical formula.
- Click Calculate to see your results.
Examples
H2O (water)
Water's formula H2O has a molecular weight of 18.015 g/mol: two hydrogen atoms (1.008 each) plus one oxygen atom (15.999).
Ca(OH)2 (calcium hydroxide)
Calcium hydroxide has a molecular weight of 74.092 g/mol: one calcium atom plus two oxygen and two hydrogen atoms from the parenthesized hydroxide group.
Who should use it
- Finding the molar mass needed for a Molarity Calculator or stoichiometry problem.
- Checking chemistry homework involving molecular weight calculations.
Industry applications
- Chemistry education
- Pharmaceutical formulation and laboratory chemistry
Advantages
- Supports nested parentheses for complex ionic compounds.
- Uses standard IUPAC atomic weights for accurate results.
Limitations
- Doesn't support hydrate dot notation or isotope labeling.
Common mistakes to avoid
- Using the wrong capitalization for element symbols — "CO" (carbon + oxygen) is very different from "Co" (cobalt).
- Forgetting a closing parenthesis in a grouped formula, which the calculator will flag as mismatched.
Best practices
- Double-check element capitalization carefully — the first letter is always uppercase and any second letter is always lowercase.
Tips
- Once you have the molecular weight, plug it directly into the Molarity Calculator's "molar mass" field to go straight from formula to solution concentration.