Percent Yield Calculator
Enter the yield you actually collected and the theoretical yield from stoichiometry. The calculator applies percent yield = actual ÷ theoretical × 100 and shows every step.
Example: with Actual yield (g) 4.32 · Theoretical yield (g) 5.4 → Percent yield: 80.0%.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outHow to calculate percent yield
The percent yield equation compares what you collected with what the balanced equation says was possible: percent yield = (actual yield ÷ theoretical yield) × 100. Both must be in the same unit, and the theoretical yield must come from limiting-reagent stoichiometry, not from the mass of reactant you started with. Worked example: an aspirin synthesis with a theoretical yield of 5.40 g that delivers 4.32 g of dry product has a percent yield of 4.32 ÷ 5.40 × 100 = 80%.
Real yields land under 100% because of side reactions, incomplete conversion, and product left behind during transfers and purification. A result over 100% is a red flag, not a bonus: the usual culprits are a still-wet product, impurities adding mass, or a units slip between actual and theoretical — this calculator flags it so you can recheck before writing it up.
How it’s calculated
Percent yield = actual yield ÷ theoretical yield × 100, with both yields in the same unit (grams here). The “not recovered” row is theoretical − actual, also expressed as a percentage of theoretical. Yields above 100% are labeled as a data or purity problem rather than treated as valid, since a reaction cannot produce more product than stoichiometry allows.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Using the starting reactant mass as the theoretical yield — theoretical yield comes from limiting-reagent stoichiometry on the product.
- Mixing units, like an actual yield in mg against a theoretical yield in g — convert both to the same unit first.
- Celebrating a yield over 100% — it almost always means wet or impure product, or a weighing or units error.
Frequently asked questions
How do I calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. If you collected 12.5 g but stoichiometry predicted 15 g, the percent yield is 12.5 ÷ 15 × 100 = 83.3%.
What is the percent yield equation?
Percent yield = (actual yield ÷ theoretical yield) × 100. Actual is what you weighed after purification; theoretical is the maximum mass the limiting reagent could form.
Can percent yield be more than 100%?
Not physically. A calculated yield above 100% means the product still holds solvent or moisture, contains impurities, or one of the two numbers is wrong — re-dry, re-weigh, and recheck units.
What is the difference between actual and theoretical yield?
Theoretical yield is calculated from the balanced equation and the limiting reagent; actual yield is the mass you really isolate. Actual is almost always smaller because of side reactions and handling losses.
Is percent yield the same as percent error?
No. Percent yield is actual ÷ theoretical × 100, while percent error is |measured − accepted| ÷ accepted × 100 — an 80% yield corresponds to a 20% shortfall, not a 20% error in measurement.