Percent Yield Calculator
No real chemical reaction converts 100% of its reactants into the desired product — percent yield measures exactly how close to that theoretical maximum a real reaction actually got.
Inputs
Result
81.32%
Lost 1.7 g
How the percent yield calculator works
Percent yield = (actual yield ÷ theoretical yield) × 100.
Mass 'lost' = theoretical yield − actual yield, representing product that wasn't successfully recovered.
Worked example: actual yield 7.4 g, theoretical yield 9.1 g
- Percent yield = (7.4 ÷ 9.1) × 100 ≈ 81.32%.
- Mass lost = 9.1 − 7.4 = 1.7 g.
Common mistakes to avoid
Assuming a percent yield below 100% indicates an error in the experiment
Some yield loss is normal and expected in virtually every real reaction, due to side reactions, incomplete reactions, purification losses, or minor measurement imprecision — a percent yield in the 80-95% range is often considered quite good for many real laboratory procedures, not a sign something went wrong.
Confusing theoretical yield with actual reactant mass used
Theoretical yield specifically means the maximum possible product mass predicted by stoichiometry (based on the limiting reactant), not simply the mass of reactant that was originally used — these are related through the reaction's mole ratios, not directly equal to each other.
Frequently asked questions
Why do real reactions rarely achieve 100% yield?
Common real-world causes include incomplete reactions (not all reactant converts), competing side reactions consuming some reactant into unwanted products, and physical product losses during transfer, filtration or purification steps.
How is theoretical yield calculated in the first place?
It's derived from the balanced chemical equation's mole ratios, applied to whichever reactant is the limiting reagent — this calculation happens separately, upstream of the percent yield calculation, which simply compares that predicted maximum against what was actually obtained.
What's considered a 'good' percent yield?
This varies enormously by reaction type and complexity — some straightforward reactions routinely achieve 90%+ yield, while complex multi-step syntheses might be considered successful at 50% or even lower, depending on the specific chemistry involved.
Can percent yield ever exceed 100%?
In principle it shouldn't for a correctly measured reaction, but it can appear to in practice if the product is contaminated with an impurity adding extra mass, or if there's a measurement error — a yield over 100% is usually a signal to double-check purity or measurement accuracy, not a genuine result exceeding the theoretical maximum.
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