Stoichiometry calculator
Grams to moles to grams, limiting reactant, excess left over and percent yield, with every step shown.
How stoichiometry works
Every stoichiometry problem goes through moles. Convert what you know to moles (grams ÷ molar mass, particles ÷ 6.022 × 10²³, liters of gas at STP ÷ 22.4, or molarity × liters of solution). Then use the mole ratio from the balanced equation to get moles of what you want, and convert back to the unit you need.
Limiting reactant
When you know the amounts of two or more reactants, divide each one’s moles by its coefficient. The smallest result belongs to the limiting reactant: it runs out first and sets how much product forms. The other reactants are in excess, and the tool shows how much of each is left over.
Theoretical and percent yield
The theoretical yield is the most product the limiting reactant can make. Percent yield compares what you actually got in the lab: percent yield = actual yield ÷ theoretical yield × 100. Open the percent yield section to add your actual yield.
Significant figures
Results are rounded to the fewest significant figures among the amounts you entered. Molar masses use standard atomic weights and are treated as exact enough not to limit the answer.