Percent Yield Calculator
Percent yield is the standard way chemists judge how well a reaction performed. It compares how much product you actually isolated, the actual yield, against the most the reaction could possibly have produced, the theoretical yield set by the balanced equation and the limiting reactant. Expressed as a percentage, it captures everything that went right or wrong between the flask and the final weighed product: side reactions that consumed reactant, product that stayed in solution or clung to the glass, and reactions that stopped short of completion. A high percent yield signals a clean, efficient synthesis; a low one tells you to hunt for where material was lost. This calculator does the arithmetic instantly. Enter the actual yield you measured and the theoretical yield you calculated from stoichiometry, in the same units, and it returns the percent yield to two decimal places. A result above 100% is a warning that the product may still be wet with solvent or contaminated, or that a calculation slipped, so it pays to recheck. Every figure is computed deterministically from the standard yield formula, with a worked example below that reconciles exactly to the calculator so you can follow each step.
Percent yield compares what you made to what was possible: percent yield = (actual / theoretical) x 100. An actual yield of 8.5 g against a theoretical 10 g is a percent yield of 85.00%, a clean and efficient reaction.
Percent yield formula
percent yield = (actual yield / theoretical yield) x 100
actual yield = mass of product obtained
theoretical yield = maximum mass from the limiting reactant
both yields in the same units (grams or moles)
The theoretical yield comes from the balanced equation and the limiting reactant. The actual yield is what you weigh out. Their ratio, scaled to a percentage, is the percent yield.
Worked example
A reaction has a theoretical yield of 10 g, and you isolate 8.5 g of product.
- Ratio = 8.5 / 10 = 0.85.
- Percent yield = 0.85 x 100 = 85.
- Percent yield = 85.00%.
These are the calculator's default inputs, so the result above matches the widget exactly.
Percent yield calculator: frequently asked questions
What is percent yield?
Percent yield measures how efficient a chemical reaction was by comparing the amount of product you actually obtained, the actual yield, against the maximum the stoichiometry predicts, the theoretical yield. It is expressed as a percentage. A high percent yield means little product was lost to side reactions, incomplete conversion or handling.
Why is percent yield usually below 100%?
Real reactions rarely convert every molecule of reactant into the desired product. Some reactant is lost to competing side reactions, some product stays dissolved or stuck to glassware, and some reactions reach equilibrium before completion. Each loss lowers the actual yield below the theoretical maximum.
Can percent yield exceed 100%?
In principle no, because you cannot make more product than the limiting reactant allows. A figure above 100% almost always signals that the product was not fully dried and still contains solvent or impurities, or that a weighing or theoretical-yield calculation was wrong. It is a red flag to recheck the work.
How do I find the theoretical yield?
Identify the limiting reactant, use the balanced equation to find the moles of product it can form, then convert moles of product to mass using its molar mass. That mass is the theoretical yield. Standard atomic weights for the conversion are published by the National Institute of Standards and Technology.
What is the percent yield formula?
Percent yield equals the actual yield divided by the theoretical yield, times 100. Both yields must be in the same units, usually grams or moles. For example, 8.5 grams obtained against a 10 gram theoretical maximum is 85% yield.
Official sources
- Atomic weights and chemical reference data for stoichiometry: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.