Limiting Reactant Calculator

About this calculator

In a chemical reaction, reactants are almost never combined in the exact stoichiometric ratio the balanced equation calls for. The limiting reactant is the one that runs out first, stopping the reaction and capping the maximum amount of product that can form — the other reactant is left over in excess. Identifying it is one of the first steps in any stoichiometry problem, because product yield calculations depend entirely on the limiting reagent's quantity, not the total amount of chemicals mixed together.

This calculator finds the limiting reactant by dividing each reactant's moles by its coefficient in the balanced equation and comparing the resulting ratios — whichever reactant gives the smaller ratio is limiting. This method is taught in every introductory chemistry course and used routinely by chemists and chemical engineers to plan reagent quantities, minimize waste, and predict theoretical yield before running a reaction in the lab or scaling it up industrially.