Molecular Weight Calculator: Chemical Formula Parser

This molecular weight calculator parses any chemical formula you type. NaCl, $\text{H}_2\text{O}$, $\text{C}_6\text{H}_{12}\text{O}_6$, Mg(OH)2, or hydrates like CuSO4·5H2O, and returns the molecular weight in g/mol. It multiplies each element's atomic weight (IUPAC 2021 standard values) by the number of atoms in the formula, then sums the results. A Live Audit table appears as you type, listing every element, its count, unit atomic mass, total mass contribution, and mass percentage. The periodic-table reference below the input lets you click elements directly into the formula field, which is useful when you don't remember exact symbols. Results are ready for stoichiometry, molarity calculations, or lab solution preparation. The tool does not require sign-up; all parsing and arithmetic run in your browser.

Type a chemical formula into the input field using standard notation: uppercase first letter, lowercase second, numbers for subscripts. For example, type H2O for water, NaCl for sodium chloride, or C6H12O6 for glucose. Wrap repeating groups in parentheses followed by a count. Mg(OH)2 gives one magnesium, two oxygen, and two hydrogen. For hydrates, use a middle dot or asterisk: CuSO4·5H2O or CuSO4*5H2O. As you type, the Live Audit table updates to show each element, how many atoms appear, the unit atomic mass (IUPAC 2021), the total mass from that element, and its percentage of the overall molecular weight. The final molecular weight in g/mol appears at the top of the result. You can click elements on the periodic-table reference to insert them, and the result is ready to copy into a molarity or stoichiometry calculation.

Multiply each element’s atomic weight by its count in the formula, then add. Water: $2 \times 1.008 + 15.999 \approx 18.015$ g/mol. Glucose: $6 \times 12.011 + 12 \times 1.008 + 6 \times 15.999 \approx 180.16$ g/mol. The calculator shows a Live Audit. Element, Count, Unit Mass, and Total Mass %, as you type.

Numbers after elements are subscripts: H2O, C6H12O6. Parentheses with a multiplier apply to the whole group: Mg(OH)2 gives 1 Mg, 2 O, 2 H. For hydrates, use a middle dot or asterisk. CuSO4·5H2O or CuSO4*5H2O, so the water molecules add to the main compound. Unicode subscripts (₆, ₁₂) work and are converted automatically.

Molecular weight shows up in molarity ($M = m/(MW \times V)$), stoichiometry, and solution prep. Use this calculator to get MW, then plug it into the Molarity Calculator when you need concentration from mass and volume.