Stoichiometry Calculator
Convert between moles, grams, and number of molecules/atoms using molar mass. The foundation of stoichiometric calculations.
Results
What is it?
Stoichiometry is the quantitative study of reactants and products in chemical reactions. The mole is the SI unit of amount of substance — one mole contains exactly 6.022 × 10²³ particles (Avogadro's number, Nₐ). The molar mass (g/mol) numerically equals the molecular weight in atomic mass units (u). This calculator converts freely between moles, grams, and molecule counts.
How to use
Enter the molar mass of your substance (sum of atomic masses from the periodic table). Enter the known quantity and select its unit (moles, grams, or ×10²³ molecules). All three representations are computed simultaneously.
Example scenario
Water (H₂O) has a molar mass of 18.015 g/mol (2×1.008 + 15.999). Enter molar mass = 18.015, quantity = 2 mol. Result: 2 mol × 18.015 = 36.03 g of water, containing 2 × 6.022 × 10²³ ≈ 12.044 × 10²³ molecules.
Pro tip
Key molar masses for reference: H₂O = 18.015, NaCl = 58.44, CO₂ = 44.01, O₂ = 32.00, H₂SO₄ = 98.08, CaCO₃ = 100.09 g/mol. In a balanced reaction like 2H₂ + O₂ → 2H₂O, the molar ratios (2:1:2) directly tell you quantities. This is the limiting reagent concept — the reactant that runs out first determines the maximum product yield.