Chemical Equation Stoichiometry Calculator

Stoichiometry is the calculation of relative quantities of reactants and products in chemical reactions using the mole ratios from a balanced equation. The word comes from Greek: stoicheion (element) + metron (measure). It answers "how much of each substance is consumed or produced?" when given an amount of one substance.

Convert the known mass to moles (divide by molar mass), then multiply by the mole ratio from the balanced equation, then convert to mass (multiply by the product molar mass). For 2H₂ + O₂ → 2H₂O: if you start with 4 g H₂ (about 2 mol), the ratio says you produce about 2 mol H₂O, which is roughly 36 g of water.

The limiting reagent is the reactant that runs out first and determines the maximum amount of product. Find it by converting each reactant to moles, then dividing by its stoichiometric coefficient: the smaller result is the limiting reagent. The excess reagent is the other reactant; some is left over after the reaction completes.

Theoretical yield is the maximum amount of product stoichiometry predicts if the limiting reagent reacts completely with no losses. Actual yield is the amount you physically recover, which is always lower because of side reactions, incomplete conversion, and losses during transfer and purification. Percent yield = (actual / theoretical) × 100. For example, if the theoretical yield is 35.75 g of water and you recover 32 g, the percent yield is (32 / 35.75) × 100 = 89.5%. Use this calculator to get the theoretical yield, then divide your measured mass by it to find percent yield.

No. This tool computes stoichiometry from an equation you have already balanced, so you enter the balanced coefficients yourself. To balance an equation, adjust the coefficients until each element has the same number of atoms on both sides, starting with the most complex molecule and leaving free elements like O₂ or H₂ for last. Once every element balances, enter those coefficients here to find the moles, grams, and molecules of each substance.