Stoichiometry Calculator

Enter molar mass and any one of moles, grams, or molecules to find the others.

Molar mass (g/mol)

Moles

Grams

Molecules

Moles —

Grams —

Molecules —

Moles = grams / molar mass. Molecules = moles × 6.022 × 10²³ (Avogadro’s number).

🛒 Shop related: Lab glassware · pH meters · Lab supplies
Affiliate links — we may earn a commission at no cost to you. Learn more

Get your results + weekly chemistry tips

One email per week. Tips, tool deals, new calculators. Unsubscribe anytime.

Free tools, useful tips. We recommend products we'd actually use.

Mole-Gram-Molecule Conversions

Stoichiometry is the calculation of quantities in chemical reactions. The mole is the bridge between the atomic scale and the lab scale.

One mole of any substance contains 6.022 × 10²³ particles (Avogadro’s number) and has a mass in grams equal to its molar mass.

Stoichiometry uses balanced chemical equations to relate moles of reactants and products. The ratio of coefficients in the balanced equation directly gives the mole ratio. For 2H₂ + O₂ → 2H₂O: 2 moles of H₂ react with 1 mole of O₂ to produce 2 moles of H₂O. The mole ratio H₂:O₂:H₂O = 2:1:2.

Limiting reagent: the reactant that runs out first determines the maximum product yield. Given 4.0g H₂ (2.0 mol) and 40.0g O₂ (1.25 mol): 2.0 mol H₂ requires 1.0 mol O₂. You have 1.25 mol O₂ — excess. H₂ is the limiting reagent. Maximum H₂O produced = 2.0 mol H₂ × (2 mol H₂O / 2 mol H₂) = 2.0 mol H₂O = 36.0g.

Mole calculation pathway: grams → moles (÷ molar mass) → mole ratio → moles of target → grams (× molar mass). Always write molar mass in g/mol units and apply dimensional analysis to verify units cancel correctly.

This calculator applies to ideal complete reactions in solution or gas phase. Real reactions may be incomplete (percent yield < 100%), have competing side reactions, or involve non-stoichiometric intermediates. Use the reaction yield calculator after completing stoichiometric calculations to account for real-world losses.