Chemical Reaction Yield Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/6/2026
A chemical reaction's yield is calculated with (actual mass ÷ theoretical mass) × 100. For an actual mass of 8.5 g and a theoretical mass of 10 g, the yield is 85%.
Explanation
A chemical reaction's yield compares the amount of product actually obtained in the lab to the maximum amount the reaction's stoichiometry would theoretically allow, if the reaction were complete and lossless. The theoretical mass is calculated from the amounts of reactants used, the stoichiometric coefficients of the balanced equation, and the molar masses of the species involved — a separate calculation to perform beforehand, before using this calculator. In practice, the actual yield is almost always below 100%, for several common reasons: the reaction isn't complete (a chemical equilibrium remains), side reactions consume part of the reactants, or product is lost during purification steps (filtration, recrystallization, transfer between containers). A high yield (above 90%) is generally considered good in synthetic chemistry, while a lower yield, without necessarily being an experimental error, often prompts a review of the protocol or operating conditions (temperature, duration, reactant purity).
Example: actual mass 8.5 g, theoretical mass 10 g
Inputs
Actual mass obtained: 8.5 g. Theoretical mass expected: 10 g.
Calculation
Yield = (8.5 ÷ 10) × 100 = 85%.
Result
This reaction's yield is 85%.
Frequently asked questions
Is a yield above 100% possible?
In theory no, but a calculated result slightly above 100% sometimes happens in practice, generally due to impurities remaining in the weighed product (residual solvent, unreacted reagent) that artificially inflate the measured mass, or an error in calculating the initial theoretical mass.
How is the expected theoretical mass calculated?
It's determined from the reaction's balanced equation, the limiting reactant (the one present in insufficient quantity for the reaction to go to full completion), and the molar masses of the species involved, via the equation's stoichiometric coefficients. This calculation is done beforehand, before using this calculator, which simply compares that theoretical result to the mass actually obtained.
Why is the actual yield almost always below 100%?
Several factors commonly contribute: an incomplete reaction (a chemical equilibrium not fully shifted), side reactions that consume some reactants toward unwanted products, and material losses during purification or transfer steps between containers. A 100% yield would assume a perfect, lossless reaction, a rare case in laboratory practice.