Molecular Mass Calculator – Online Enter Formula H2O

Molecular mass (also called molecular weight) is the sum of the atomic masses of all atoms in a molecule. It is calculated by multiplying the atomic mass of each element by the number of atoms of that element in the chemical formula, then summing all contributions. For example, H₂O has 2 hydrogen atoms (2 × 1.008 = 2.016) and 1 oxygen atom (1 × 15.999 = 15.999), giving a total of 18.015 g/mol. The unit is grams per mole (g/mol), also expressed in Daltons (Da) or atomic mass units (amu).

While often used interchangeably, there are subtle differences: Molecular mass refers to the mass of a single molecule (measured in amu or Da). Molar mass is the mass of one mole (6.022 × 10²³ molecules) of a substance, measured in g/mol — numerically identical to molecular mass. Formula mass is used for ionic compounds (like NaCl) that don't form discrete molecules, calculated from the empirical formula. For most practical purposes, the numerical value is the same across all three terms.

Use parentheses () to group atoms that repeat as a unit. For example, magnesium hydroxide is written as Mg(OH)2 — meaning one Mg atom plus two OH groups (2 O atoms and 2 H atoms). For hydrated compounds, use the middle dot · to separate the anhydrous part from water molecules: CuSO4·5H2O represents copper(II) sulfate pentahydrate. You can also use square brackets [] for coordination compounds like K4[Fe(CN)6]. The calculator supports nested parentheses and multiple hydrate groups.

This calculator includes over 80 common elements from the periodic table, covering all major main-group elements, transition metals, and several lanthanides/actinides. Atomic masses are based on IUPAC standard atomic weights and are provided to 3–4 significant decimal places. For elements with multiple stable isotopes (like chlorine, Cl = 35.45), the weighted average is used. If you enter an unsupported element symbol, the calculator will alert you with an error message so you can double-check your formula.

Absolutely! While the term "molecular mass" technically applies to molecules, this calculator works perfectly for ionic compounds, salts, and minerals. Enter the formula just as you would for any compound — for example, NaCl for table salt (58.44 g/mol), CaCO3 for calcium carbonate (100.09 g/mol), or K2SO4 for potassium sulfate (174.26 g/mol). The calculator ignores any charges (like + or -) since they don't affect the mass. For crystalline hydrates, use the middle-dot notation as described above.

Knowing the molecular mass is essential for many scientific and practical applications: Stoichiometry — calculating reactant and product quantities in chemical reactions; Solution preparation — making molar solutions in laboratory settings; Pharmaceutical formulation — determining precise drug dosages; Environmental analysis — measuring pollutant concentrations; and Industrial chemistry — optimizing production yields. Whether you're a student, researcher, or professional, accurate molecular mass values are fundamental to quantitative chemistry.