Calculate the molecular (molar) weight of a chemical compound automatically from its formula, such as H2O, NaCl, or Ca(OH)2.
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The molecular weight (or molar mass) of a chemical compound is the sum of the atomic masses of all the atoms making up one molecule of that compound, in grams per mole. This calculator automatically calculates molecular weight from the written chemical formula (such as H2O, NaCl, or C6H12O6), by parsing each element symbol and its following number (the count of atoms of that element), multiplying each count by its corresponding atomic mass from the periodic table, then summing all the results. The calculator also supports parentheses for grouping a set of atoms with a shared multiplier (such as Ca(OH)2, where the OH group repeats twice), and hydrate formulas that contain bound water molecules (such as CuSO4·5H2O, written after a dot or center-dot). Illustrative example: water H2O contains two hydrogen atoms (1.008 × 2) and one oxygen atom (15.999), giving it a molecular weight of approximately 18.015 g/mol. This calculation is used primarily in converting mass to moles and vice versa, and in preparing solutions with a precise concentration.
A chemical formula like C6H12O6 (glucose) packs a surprising amount of information into a short string of letters and numbers, and correctly calculating its molecular weight requires systematically parsing that formula into its component parts before doing any arithmetic.
The basic parsing logic reads each element symbol (a single capital letter, or a capital letter followed by a lowercase letter, since element symbols follow this exact convention to avoid ambiguity) along with any number immediately following it, which indicates how many atoms of that element appear in the formula. When no number follows a symbol, exactly one atom of that element is implied — this is why H2O is read as two hydrogens and one (implied single) oxygen, not two hydrogens and zero oxygens.
Parentheses add a layer of grouping to this parsing: a formula like Ca(OH)2 means the entire OH group inside the parentheses repeats twice, giving one calcium atom, two oxygen atoms, and two hydrogen atoms total — correctly handling this requires multiplying every element's count inside the parentheses by the number following the closing parenthesis, not just multiplying a single adjacent atom.
Hydrate formulas introduce another common but sometimes overlooked complexity: compounds like CuSO4·5H2O include water molecules chemically bound within the crystal structure, indicated by a center-dot followed by a coefficient and H2O. These bound water molecules genuinely contribute to the compound's total molecular weight and must be included in the calculation — omitting the hydrate water, a common calculation mistake, would give a molecular weight matching only the anhydrous (water-free) form of the compound rather than the actual hydrated crystal being weighed on a laboratory balance.
Getting molecular weight right matters enormously in practice because it's the direct conversion factor between the mass a chemist actually weighs out on a balance and the number of moles that mass represents — an error in molecular weight calculation propagates directly into every subsequent calculation involving that substance, from how much of it is needed for a reaction to what concentration results when it's dissolved into a specific volume of solution.
Any formula using standard element symbols and subscript numbers, including parentheses for grouped atoms (like Ca(OH)2) and a dot before hydrate water molecules (like CuSO4·5H2O or CuSO4.5H2O).
Double-check that element symbols use correct capitalization (Na, Cl, not NA or CL), that every open parenthesis has a matching close parenthesis, and that there are no extra spaces or typos inside the formula.
The calculator uses standard atomic weights consistent with the periodic table (IUPAC-style values), covering the elements most commonly found in everyday chemical formulas.