Chemistry overview
What is percent yield?
Percent yield measures how much product a reaction actually produces compared with the maximum amount predicted by stoichiometry.
The calculation helps evaluate reaction efficiency, product recovery, and the difference between an ideal chemical model and an experimental result.
Formula
Percent-yield formula
Percent yield= actual yield ÷ theoretical yield × 100
- Actual yield is the measured amount of product recovered.
- Theoretical yield is the maximum amount predicted from stoichiometry.
- Both yields must describe the same product and use compatible units.
Calculation method
How to calculate percent yield
- Determine the actual amount of product obtained.
- Calculate or identify the theoretical product amount.
- Confirm that both yields use the same unit.
- Divide actual yield by theoretical yield.
- Multiply the ratio by 100.
Worked example
Percent yield chemistry example
A reaction produces 36.03 g of product. Stoichiometry predicts a theoretical yield of 40 g.
- Divide actual by theoretical yield: 36.03 ÷ 40 = 0.90075
- Multiply by 100: 0.90075 × 100 = 90.075%
The reaction therefore produced 90.075% of the theoretical product amount.
Required input
How to find theoretical yield
Theoretical yield normally comes from a balanced equation, the limiting reactant, mole ratios, and the product molar mass.
Identify the reactant that limits product formation with the Limiting Reactant Calculator, then calculate the expected product amount using the Stoichiometry Calculator.
Result interpretation
Why percent yield can exceed 100%
A calculated yield above 100% does not mean that a reaction created more pure product than stoichiometry permits.
Common causes include retained water or solvent, contamination, incomplete drying, weighing errors, product impurities, or an underestimated theoretical yield.
Experimental factors
What affects percent yield?
- Incomplete reaction or insufficient reaction time.
- Competing side reactions.
- Product loss during filtration, transfer, washing, or purification.
- Impure starting materials.
- Measurement and balance uncertainty.
- Product decomposition or evaporation.
Common errors
Common percent-yield mistakes
- Reversing actual and theoretical yield.
- Using yields expressed in different units.
- Calculating theoretical yield from the excess reactant.
- Using an unbalanced chemical equation.
- Treating wet or contaminated product as pure product.
- Rounding intermediate results too early.
Calculation limits
Assumptions and limitations
The actual and theoretical yields must refer to the same product and use compatible units. The theoretical yield must be greater than zero.
Percent yield reports product recovery, but it does not independently identify purity, selectivity, measurement quality, or the cause of material loss.
A high percent yield can still represent an impure product, while a low value can result from reaction inefficiency, handling loss, or analytical error.
Supporting tools
Complete the reaction analysis
Find molar mass with the Molecular Weight Calculator, or compare a measured value with a trusted reference using the Percent Error Calculator.
Questions and answers
Percent yield calculator FAQ
What is percent yield?
Percent yield compares the amount of product obtained experimentally with the maximum theoretical amount predicted by stoichiometry.
What formula does the percent yield calculator use?
It divides actual yield by theoretical yield and multiplies the ratio by 100.
Can percent yield be greater than 100%?
Yes, but a result above 100% usually indicates impurities, retained solvent, measurement error, incomplete drying, or an incorrect theoretical yield.
Do actual and theoretical yield need the same unit?
Yes. Both quantities must represent the same substance and use compatible units because their units cancel in the ratio.
Is percent yield the same as percent error?
No. Percent yield compares actual product with theoretical product, while percent error compares an experimental measurement with an accepted reference value.