Percent Yield Calculator

Percent yield compares how much product you actually obtained to the maximum theoretically possible.

Formula:

% yield = (actual yield / theoretical yield) × 100

Theoretical yield is the maximum amount of product calculated from stoichiometry, assuming the limiting reagent is completely consumed and no product is lost.

Actual yield is what you physically collect after the reaction and purification.

Why is percent yield rarely 100%? Real reactions rarely produce 100% yield due to:

• Incomplete reaction: Equilibrium limits products formed
• Side reactions: Other products form alongside the desired product
• Product loss: During transfer, filtration, crystallization, or distillation
• Impure reagents: Contaminated starting materials
• Measurement errors: Losses during weighing or handling

Typical yield ranges in different fields:

That pharmaceutical row is the one worth staring at. Yields multiply down a route, so eight steps at 60% each land at 1.7% overall. It is why process chemists will spend months on a single step that everyone else considers finished.

Atom economy (related concept): Even with 100% yield, a reaction may waste atoms if large byproducts are formed. Atom economy = MW of desired product / total MW of the reactants × 100

For a balanced equation the reactant masses and the product masses are equal, so dividing by the total mass of all products gives the same number. Our atom economy calculator takes the products form, since the byproducts are usually the easier side to enumerate.

For green chemistry, high atom economy is just as important as high percent yield.

Theoretical yield comes first

Percent yield is meaningless until the theoretical yield is right, and that number comes from the limiting reagent rather than from whichever reactant you happened to weigh out. Work out the moles of each reactant, divide each by its coefficient in the balanced equation, and the smallest result identifies the limiting reagent. Everything else is in excess and will be left over.

Getting this wrong is the usual reason a percent yield comes out absurd. Calculate against a reagent that was in excess and the theoretical figure is too large, so a perfectly good reaction reports a disappointing 40%.

What a yield above 100% really means

It is never a reaction that overperformed. In practice it is one of three things: the product is still wet with solvent and you weighed the solvent too, an impurity has been carried through the workup, or the theoretical yield was calculated with the wrong molar mass. Drying the sample to constant weight settles the first case, and it is the commonest by a wide margin.

Reported yields in the literature are usually of purified, characterized product, which is why a paper’s 85% and an undergraduate’s 85% are not always the same claim.