This percent yield calculator finds how efficient a chemical reaction was: percent yield = actual yield ÷ theoretical yield × 100. Enter any two of the three values and get the third.
What Is Percent Yield?
Percent yield compares what a reaction actually produced to the maximum it could have produced (the theoretical yield from stoichiometry). No real reaction hits 100%: side reactions, incomplete reactions, product lost during filtration and transfer, and impure reactants all take their cut. Percent yield is how chemists — from students to pharmaceutical manufacturers — measure and improve a process. This calculator is part of our Chemistry Calculators collection; the theoretical yield itself starts from amounts you can convert with the Molar Mass Calculator.
The Percent Yield Formula
Percent yield = (actual yield ÷ theoretical yield) × 100
Worked example (verified): a reaction that could produce 10.0 g of product actually gives 8.5 g after filtering and drying: percent yield = 8.5 ÷ 10.0 × 100 = 85% — a good result for a multi-step lab synthesis.
Reading Your Yield
- 90–100%: excellent — typical of simple, clean reactions and careful technique.
- 70–90%: good, normal lab range.
- Below 70%: worth investigating — incomplete reaction, side products, or product lost in workup.
- Over 100%: impossible for pure product — it means your “product” is wet or contaminated (weighing solvent counts as product until you dry it properly).
Percent Yield vs. Atom Economy vs. Percent Error
Percent yield measures your process. Atom economy measures the reaction design itself (how many reactant atoms end up in the product at all). Percent error — comparing any measurement to its accepted value — is the general tool we cover in the Percent Error Calculator. And not every “100 − yield” gram was wasted the same way: percent recovery in purification steps is tracked separately from reaction yield.
Related Tools
- Molar Mass Calculator — for theoretical yield stoichiometry
- Percent Error Calculator
- Chemistry Calculators — the full collection
Frequently Asked Questions
How do I calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. Example: 8.5 g actual ÷ 10 g theoretical = 85%.
Can percent yield be over 100%?
Not for pure, dry product. A yield over 100% signals contamination — usually solvent or water still in the sample, or an impurity counted as product.
Where does theoretical yield come from?
From the balanced equation and the limiting reactant: convert the limiting reactant’s amount to product using the mole ratio and the product’s molar mass.
Why is my percent yield low?
Incomplete reaction (equilibrium or too little time), side reactions, product solubility in the wash solvent, spills and transfer losses, or impure starting material.
What is a good percent yield?
For undergraduate labs, 70–90% is typical and respectable; industrial processes fight for every point above 95% because they run at massive scale.
Is this percent yield calculator free?
Yes — free, instant, no sign-up.