Molar Mass & Stoichiometry Calculator

Enter a chemical formula to compute its molar mass, see the element breakdown with mass percentages, and follow the step-by-step calculation. Supports parenthesized groups like Ca(OH)2.

Chemical Formula

Formula

Presets

Results

Molar Mass

18.015 g/mol

Element	Count	Atomic Mass	Subtotal	Mass %
O (Oxygen)	1	15.999	15.999	88.81%
H (Hydrogen)	2	1.008	2.016	11.19%

Mass Composition

Step-by-Step Calculation

1. Identify elements and counts

\text{Formula: } \text{H2O} \quad \Rightarrow \quad \text{O} \times 1, \quad \text{H} \times 2

2. Multiply atomic mass by count

\text{O}: 1 \times 15.999 = 15.999 \text{ g/mol}

\text{H}: 2 \times 1.008 = 2.016 \text{ g/mol}

3. Sum all contributions

M = 15.999 + 2.016 = 18.015 \text{ g/mol}

Reference Guide

What is Molar Mass

Molar mass is the mass of one mole of a substance, measured in grams per mole (g/mol). It equals the sum of the atomic masses of every atom in the formula.

M = \sum (\text{count}_i \times \text{atomic mass}_i)

Mass Percent

Mass percent tells you what fraction of the total molar mass comes from each element. It is useful for determining empirical formulas from experimental data.

\text{Mass \%} = \frac{\text{element subtotal}}{\text{molar mass}} \times 100

Parsing Chemical Formulas

Chemical formulas use element symbols and subscripts. Parentheses group atoms that repeat together, like Ca(OH)₂ which contains 1 calcium, 2 oxygens, and 2 hydrogens.

Moles and Grams

To convert between grams and moles, divide or multiply by the molar mass. One mole of any substance contains Avogadro's number of particles.

n = \frac{m}{M} \quad \text{and} \quad N_A = 6.022 \times 10^{23}