What is a limiting reactant?
In a chemical reaction, the limiting reactant is the substance that gets completely used up first, stopping the reaction and determining the maximum amount of product that can form. Any other reactant left over is called the excess reactant.
How this calculator works
Each reactant’s mass is converted to moles (moles = mass / molar mass), then divided by its coefficient in the balanced equation to normalize both reactants to the same reaction “scale.” Whichever reactant has the smaller normalized value (moles ÷ coefficient) is the limiting reactant, since it runs out first relative to what the reaction requires.
Note: Enter coefficients exactly as they appear in your balanced chemical equation for accurate results. This tool is intended for general chemistry education and planning purposes.