Molar Mass Calculator — Molecular Weight from Formula

Compute the molar mass of any compound from its chemical formula. Supports complex formulas with brackets.

About this calculator

A molar mass calculator computes the molecular weight of any chemical compound from its formula. Molar mass (in grams per mole) is the bridge between the macroscopic world of grams in a beaker and the microscopic world of moles of molecules — essential for stoichiometry, solution preparation, and any quantitative chemistry.

The calculator sums atomic masses for each element in the compound, accounting for subscripts and parenthesised groups. Atomic masses are standard atomic weights from IUPAC 2021.

Formula

M = \sum_i n_i \times A_i

  • M — Molar mass (g/mol)
  • n_i — Number of atoms of element i
  • A_i — Atomic mass of element i (g/mol)
  • Example — H₂O = 2(1.008) + 1(15.999) = 18.015 g/mol

Worked example

Inputs: Calculate molar mass of glucose, C₆H₁₂O₆

  1. Carbon: 6 × 12.011 = 72.066
  2. Hydrogen: 12 × 1.008 = 12.096
  3. Oxygen: 6 × 15.999 = 95.994
  4. Total: 180.156 g/mol
  5. So 1 mole of glucose = 180.156 grams; a 5 g/L solution = 5 / 180.156 = 0.0278 mol/L

Frequently asked questions

What is the difference between molar mass and molecular weight?

In practice they are used interchangeably. Strictly: molar mass is the mass of one mole (g/mol) of a substance; molecular weight is the dimensionless ratio of the mass of one molecule to 1/12 the mass of a carbon-12 atom (the unified atomic mass unit, u). The numerical value is identical, only the units differ.

How do I find molar mass for ionic compounds?

Add the atomic masses of all atoms in the formula unit. For NaCl: 22.99 + 35.45 = 58.44 g/mol. For ionic compounds with parentheses like Ca(OH)₂: 40.08 + 2 × (16.00 + 1.008) = 74.10 g/mol. The result is the mass of one mole of formula units (NA = 6.022 × 10²³ formula units).

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