Percent Yield Calculator
Percent yield measures the efficiency of a chemical reaction by comparing what you actually obtained to what stoichiometry predicts you should have obtained. The formula is straightforward: divide the actual yield by the theoretical yield and multiply by 100. This calculator helps chemists and students evaluate reaction performance, identify where product is being lost, and compare different reaction conditions. Enter your actual yield and the theoretical yield (both in the same units, typically grams) to find the percent yield.
Percent yield formula
% yield = (actual yield / theoretical yield) * 100
Both yields must be in the same units (grams, moles, etc.). Theoretical yield is calculated from the limiting reactant using stoichiometric mole ratios.
Understanding percent yield
- A yield of 75% means you recovered 75 g for every 100 g predicted by stoichiometry.
- Side reactions consume reactants and produce unwanted products, reducing yield.
- Purification steps such as recrystallization, filtration, and distillation inevitably lose some product.
- Equilibrium reactions that do not go to completion also limit yield.
- Atom economy is a related concept: it measures the mass of desired product relative to total mass of all products formed.
Frequently asked questions
What is percent yield?
Percent yield is the ratio of the actual yield obtained from a chemical reaction to the theoretical maximum yield predicted by stoichiometry, expressed as a percentage. A 100% yield means the reaction produced the maximum amount possible.
Why is percent yield rarely 100%?
Common reasons include incomplete reactions, side reactions that produce byproducts, product lost during purification or transfer steps, and measurement errors. Yields above 100% usually indicate impurities or measurement errors.
How do I calculate theoretical yield?
Identify the limiting reactant, convert its mass to moles using its molar mass, apply the mole ratio from the balanced equation to find moles of product, then multiply by the product's molar mass.
Can percent yield exceed 100%?
A yield greater than 100% indicates an error, most commonly that the product was not completely dried (contains solvent) or that impurities were weighed along with the product.
What is a good percent yield in the lab?
Yields of 80% to 95% are typically considered good for organic synthesis. Industrial processes often achieve 90% to 99%. Very complex multi-step syntheses may have yields of 50% or lower per step.
Official sources
- IUPAC: IUPAC Gold Book - Yield.
- ACS: ACS Green Chemistry - Atom Economy.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.