Percent Yield Calculator
Enter actual and theoretical yield in grams to instantly get percent yield.
% yield = (actual / theoretical) × 100 = (8.5 / 10) × 100 = 85.00%.
What Percent Yield Measures
Percent yield is a lab efficiency check: it compares the product you actually isolated and weighed (actual yield) against the maximum amount stoichiometry says the reaction could have produced (theoretical yield), assuming perfect conversion with no losses.
% yield = (actual / theoretical) × 100. A high percent yield (close to 100%) means the reaction and purification were efficient; a low one points to side reactions, incomplete reaction, or losses during workup -- worth investigating, not automatically a mistake.
Worked example
A reaction's stoichiometry predicts 4.5 g of product (theoretical yield). After running the reaction and purifying, 3.85 g was actually recovered.
% yield = (3.85 / 4.5) × 100 = 85.56%.
Common mistake
Swapping actual and theoretical in the formula, or comparing masses of two different substances (like comparing grams of product against grams of starting reactant instead of the reactant's predicted product mass).
Keep going
- Percent yield compares actual product to theoretical yield; the stoichiometry calculator is how you find that theoretical yield from a mole ratio in the first place. Stoichiometry Calculator
Frequently Asked Questions
What is percent yield?
Percent yield compares how much product a reaction actually produced (actual yield) to how much it should have produced if every bit of limiting reactant converted perfectly (theoretical yield): % yield = (actual / theoretical) × 100.
Why is actual yield almost always less than theoretical yield?
Real reactions lose product to side reactions, incomplete reactions, purification steps (like filtering or recrystallizing), and simple transfer losses -- spilled or stuck-to-the-glassware material. A percent yield under 100% is completely normal, not a sign of an error.
Can percent yield be over 100%?
It can be calculated as over 100%, but that usually signals a real problem: leftover unreacted starting material or solvent still weighed in with the product, or an arithmetic error in the theoretical yield. A result over 100% is worth double-checking, not just reporting.
How do I find theoretical yield?
From stoichiometry: convert the limiting reactant's amount to moles, use the balanced equation's mole ratio to find moles of product, then convert that to grams using the product's molar mass. The stoichiometry calculator on this site walks through exactly that.
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