Molar Mass Calculator

Calculate the molar mass of any chemical compound from its molecular formula. Enter a formula like H2O, C6H12O6, or Ca(OH)2 and get the precise molar mass in g/mol.

Stoichiometry

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How to Use

  1. 1
    Step 1

    Enter a chemical formula (e.g. H2O, NaCl, Ca(OH)2) into the input field.

  2. 2
    Step 2

    View the total molar mass in g/mol displayed instantly.

  3. 3
    Step 3

    Check the element-by-element breakdown showing count, mass, and percent composition.

About

The mole is the SI unit for the amount of substance. One mole contains exactly 6.02214076 x 10^23 elementary entities (Avogadro's number), as defined by the International Bureau of Weights and Measures (BIPM) in 2019.

Molar mass bridges the gap between the atomic scale and the laboratory scale. When you weigh out 18.015 grams of water, you have exactly one mole — roughly 602 sextillion molecules. This relationship, n = m/M, is the foundation of stoichiometry: the science of measuring and calculating amounts in chemical reactions.

Atomic masses used in this calculator follow the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) 2021 recommended values. Each value is a weighted average of all naturally occurring isotopes. For example, chlorine's atomic mass of 35.45 reflects the natural mixture of Cl-35 (75.76%) and Cl-37 (24.24%).

For radioactive elements without stable isotopes (technetium, promethium, and all elements beyond bismuth), the mass number of the most stable or best-characterized isotope is used instead. These values are shown in parentheses on the periodic table.

The formula parser in this tool supports standard chemical notation including parenthesized groups with subscripts, such as Mg3(PO4)2 or Al2(SO4)3. It correctly handles nested multipliers and multi-character element symbols.

FAQ

What is molar mass?
Molar mass is the mass of one mole (6.022 x 10^23 particles) of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the molecular formula. For example, the molar mass of water (H2O) is 2(1.008) + 15.999 = 18.015 g/mol.
How does the calculator handle parentheses like Ca(OH)2?
The parser recognizes parentheses and multiplies each element inside by the subscript that follows the closing parenthesis. For Ca(OH)2, it correctly calculates Ca=1, O=2, H=2, giving 40.078 + 2(15.999) + 2(1.008) = 74.092 g/mol.
What is the difference between molecular mass and formula mass?
Molecular mass applies to covalent (molecular) compounds like H2O or C6H12O6. Formula mass applies to ionic compounds like NaCl or CaCl2 that do not form discrete molecules. Both are calculated the same way — by summing atomic masses. This calculator works for both types.
What are some common molar masses?
Water (H2O): 18.015 g/mol. Sodium chloride (NaCl): 58.44 g/mol. Glucose (C6H12O6): 180.156 g/mol. Sulfuric acid (H2SO4): 98.079 g/mol. Aspirin (C9H8O4): 180.159 g/mol. Calcium hydroxide (Ca(OH)2): 74.092 g/mol.
Why is hydrogen listed as 1.008 and not exactly 1?
Atomic masses reflect the weighted average of all naturally occurring isotopes. Hydrogen is mostly H-1 (mass ~1.0078) with a tiny fraction of H-2 (deuterium, mass ~2.014). The IUPAC standard atomic weight averages these, giving 1.008 g/mol. All values in this calculator use IUPAC 2021 standard atomic weights.
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