Percent Yield Calculator
Percent yield measures how efficiently a reaction produces its intended product by comparing what you actually obtained to the maximum amount that stoichiometry predicts is possible. Values below 100% indicate losses due to side reactions, incomplete reactions, or product recovery issues, and this metric is central to evaluating and optimizing any synthetic procedure.
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Formula
% Yield = (Actual Yield / Theoretical Yield) × 100
Percent yield expresses the ratio of actual yield to theoretical yield as a percentage. Actual yield is the mass of product you isolated from the reaction. Theoretical yield is the mass calculated from stoichiometry assuming complete conversion of the limiting reagent with no side reactions. A perfect reaction would give 100%, but real reactions rarely achieve this due to equilibrium, side reactions, and physical losses during isolation.
How to use the Percent Yield Calculator
- 1
Enter your actual yield
Value should be in g.
- 2
Enter your theoretical yield
Value should be in g.
- 3
Read your results instantly
Results update in real time as you type.
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Understanding theoretical yield
Theoretical yield is calculated from the balanced chemical equation and the amount of limiting reagent present. Start by writing the balanced equation, identify the limiting reagent, convert its mass to moles using its molar mass, then use the mole ratio from the equation to find moles of product, and finally convert back to grams using the product's molar mass. For example, if 2 moles of hydrogen react with 1 mole of oxygen to form 2 moles of water, and you start with 4 g of hydrogen (2 mol), the theoretical yield of water is 2 mol × 18.015 g/mol = 36.03 g. The theoretical yield is the ceiling — in practice, you will never exceed it under ideal conditions.
Why yields fall short of 100%
Even the most carefully executed reaction rarely achieves 100% yield. Common culprits include competing side reactions that consume the reagent without forming the desired product, reversible reactions that do not go to completion, product losses during transfer, filtration, or evaporation, and impure starting materials that reduce effective reagent amounts. Industrial processes optimize every step to maximize yield because even a few percentage points can mean millions of dollars saved or wasted at scale. In academic labs, yields of 70–90% are often considered acceptable for a single-step synthesis, while multi-step total synthesis of complex molecules may accumulate losses at each step, resulting in an overall yield of just a few percent.
Tips & Insights
Always identify the limiting reagent first
Theoretical yield is based on the limiting reagent — the reactant that runs out first. Using the wrong reagent as your basis gives an incorrect theoretical yield and a meaningless percent yield.
Dry your product before weighing
Residual solvent in an isolated solid inflates the apparent actual yield. Always dry the product to constant mass before the final weighing to get an accurate reading.
Yields above 100% signal an error
A percent yield over 100% is impossible. If you calculate one, your actual yield measurement is wrong — most likely due to retained solvent, impurities, or a weighing error. Re-examine your procedure.
Worked Examples
Aspirin synthesis lab
Percent yield = 84.44% — a reasonable result for a student aspirin synthesis with minor losses during recrystallization.
Nearly quantitative reaction
Percent yield = 98.00% — an excellent yield indicating minimal side reactions and efficient product recovery.
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Frequently Asked Questions
Can percent yield ever exceed 100%?
No. A percent yield above 100% indicates an experimental error, typically retained solvent or impurities adding mass to the isolated product, or an error in the theoretical yield calculation.
What is a good percent yield?
It depends on the reaction type. Industrial processes aim for 95%+. Multi-step organic syntheses often achieve 60–85% per step, and overall yields for complex molecules can be single digits after many steps.
How do I calculate theoretical yield?
Write the balanced equation, find the limiting reagent, convert its mass to moles, apply the mole ratio from the equation, then convert product moles to grams using its molar mass.
Does percent yield apply to non-mass measurements?
Yes. Yield can also be expressed using moles or volume instead of mass, as long as both actual and theoretical are measured in the same units.
Why is 100% yield physically impossible in many reactions?
Reactions governed by equilibrium never go fully to completion. Additionally, real-world losses during filtration, transfer, and drying make 100% recovery of product essentially unachievable in practice.
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