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Molar Mass Calculator

Calculate the molar mass of any chemical compound. Enter a chemical formula like H2O, NaCl, or Ca(OH)2 to get the molecular weight in g/mol with a step-by-step breakdown.

What is a Molar Mass Calculator?

A molar mass calculator is an essential tool for chemistry students and professionals. Molar mass (also called molecular weight) is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in a molecule's chemical formula. For example, water (H₂O) has a molar mass of 18.015 g/mol because it contains two hydrogen atoms (1.008 g/mol each) and one oxygen atom (15.999 g/mol). Knowing the molar mass is crucial for stoichiometry, solution preparation, and converting between mass and moles in chemical calculations. This free online molar mass calculator instantly computes the molecular weight of any compound and provides a detailed element-by-element breakdown.

Formula

M = \sum_{i=1}^{n} (a_i \times m_i)

Where M is the molar mass, aᵢ is the number of atoms of element i in the formula, and mᵢ is the standard atomic mass of element i.

How to Calculate

1
Write down or identify the chemical formula of the compound (e.g., H₂SO₄).
2
Identify each element in the formula and count the number of atoms of each.
3
Look up the standard atomic mass of each element from the periodic table.
4
Multiply the atomic mass of each element by the number of its atoms in the formula.
5
Sum all the individual contributions to get the total molar mass in g/mol.

Worked Examples

Molar Mass of Water (H₂O)

Input: H2O

Hydrogen (H): atomic mass = 1.008 g/mol, count = 2 → 1.008 × 2 = 2.016 g/mol
Oxygen (O): atomic mass = 15.999 g/mol, count = 1 → 15.999 × 1 = 15.999 g/mol
Total: 2.016 + 15.999 = 18.015 g/mol

Result: 18.015 g/mol

Molar Mass of Sulfuric Acid (H₂SO₄)

Input: H2SO4

Hydrogen (H): 1.008 × 2 = 2.016 g/mol
Sulfur (S): 32.06 × 1 = 32.06 g/mol
Oxygen (O): 15.999 × 4 = 63.996 g/mol
Total: 2.016 + 32.06 + 63.996 = 98.072 g/mol

Result: 98.072 g/mol

Molar Mass of Calcium Hydroxide (Ca(OH)₂)

Input: Ca(OH)2

Calcium (Ca): 40.078 × 1 = 40.078 g/mol
Oxygen (O): 15.999 × 2 = 31.998 g/mol
Hydrogen (H): 1.008 × 2 = 2.016 g/mol
Total: 40.078 + 31.998 + 2.016 = 74.092 g/mol

Result: 74.092 g/mol

Frequently Asked Questions

Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance. It is expressed in grams per mole (g/mol) and is numerically equal to the molecular weight of the compound.

To find the molar mass, look up the atomic mass of each element in the compound, multiply each by the number of atoms of that element in the formula, and add all the products together.

Molar mass and molecular weight are often used interchangeably. Technically, molar mass is the mass per mole of substance (in g/mol), while molecular weight is a dimensionless quantity. Numerically, they are the same.

Parentheses in a formula indicate a group of atoms that is repeated. Multiply the subscript outside the parentheses by each element inside. For example, Ca(OH)₂ means Ca × 1, O × 2, H × 2.

Molar mass is essential for converting between grams and moles, which is fundamental to stoichiometric calculations, preparing solutions of specific concentrations, and understanding reaction yields.

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