Stoichiometry Calculator

Stoichiometry is the arithmetic of a balanced chemical equation: it tells you exactly how much product a given amount of reactant can theoretically produce. This calculator walks the standard mass-to-mass path — divide the reactant mass by its molecular weight to get moles of reactant, multiply by the mole ratio (the coefficient of product over the coefficient of reactant, read straight off the balanced equation) to get moles of product, then multiply by the product's molecular weight to convert back to grams. Every step is a unit conversion chained through the mole, which is why getting the molecular weights right — using the actual formula weight of the specific reactant and product in your reaction, not a rounded textbook value — matters more than any other input here.

The optional actual-yield field turns the theoretical number into a percent yield, the ratio lab chemists actually report: real reactions never hit 100% because of side reactions, incomplete conversion, or product lost during workup, so percent yield is a measure of how efficiently your specific run performed, not a property of the reaction itself. The most common way to misuse this tool is plugging in the wrong mole ratio — it must be product coefficient divided by reactant coefficient from the balanced equation, not the other way around, and it changes for every different reactant-product pair even within the same reaction. Also remember this calculates one reactant's contribution in isolation; if a reaction has a limiting reagent among several reactants, you need to run this separately for each candidate and take the smaller resulting product mass as the true theoretical yield.