Percent yield calculator

How do I calculate percent yield?

Percent yield = actual yield ÷ theoretical yield × 100. Getting 8 g of product when the reaction could make 10 g is an 80% yield.

What is theoretical yield?

The most product the reaction could make from the limiting reactant, worked out from the balanced equation and molar masses.

Why is the actual yield lower?

Incomplete reactions, side reactions and product lost while filtering, transferring or purifying.

Can percent yield be over 100%?

Only when something is wrong — usually the product is still wet or contains impurities that add mass.

How do I find the actual yield I should expect?

Multiply the theoretical yield by the expected percent: 80% of 10 g is 8 g. Pick "Actual yield" to do it.

How do I work out the theoretical yield?

Balance the equation, convert each reactant’s mass to moles, and divide the moles by that reactant’s coefficient; the smallest quotient marks the limiting reactant. Multiply it by the product’s coefficient to get moles of product, then by the product’s molar mass for grams. The stoichiometry calculator and the limiting reactant calculator do these steps; the result is the theoretical yield to enter here.

Do both yields have to be in the same unit?

Yes. Percent yield is a ratio, and the units cancel only if the actual and theoretical yields are both in grams, both in moles, or both in the same unit of volume for a gas (OpenStax Chemistry 2e, section 4.4). Mixing grams with moles gives a meaningless percentage.

Is percent yield the same as purity?

No. Percent yield compares the amount you obtained with the most the reaction could have given. Purity says what fraction of the obtained material is the compound you want. A sample can be 95% pure and still be only a 40% yield, and an impure sample can make the yield look higher than it really is.

The formula and its terms

The actual yield is the amount of product you really collect. The theoretical yield is the maximum amount the balanced equation allows from the limiting reactant, the one that runs out first (OpenStax Chemistry 2e, section 4.4). The percent yield is the actual yield divided by the theoretical yield, times 100. The actual yield is usually lower because side reactions make other products, some reactions do not go to completion, and some product is lost when it is collected, filtered or transferred. Nothing in the calculation corrects for those losses; the percentage simply reports them.

Worked examples

OpenStax Example 4.13 reacts 1.274 g of copper(II) sulfate with excess zinc: CuSO₄ + Zn → Cu + ZnSO₄. The copper sulfate is the limiting reactant, so the theoretical yield is 1.274 g ÷ 159.6 g/mol × 63.55 g/mol = 0.5072 g of copper. If 0.392 g of copper is actually collected, the percent yield is 0.392 ÷ 0.5072 × 100 = 77.3%. A second case from the same section: 32.9 g of CCl₄ with excess HF gives a theoretical 25.9 g of CF₂Cl₂; an actual 12.5 g is a 48.3% yield. To reproduce either, enter the two masses in this calculator; the theoretical figure comes from the stoichiometry step above.

Common mistakes

The commonest mistake is computing the theoretical yield from the wrong reactant. In Example 4.12, 2.00 g of silicon and 1.50 g of nitrogen make silicon nitride, 3Si + 2N₂ → Si₃N₄. Silicon is limiting and allows 3.33 g of product; starting from nitrogen would suggest 3.76 g, and a percent yield computed against that figure would be too low. Next is using an unbalanced equation, which gives the wrong mole ratio. A third is reporting a yield above 100% without looking for the cause: the product is often wet, still holds solvent, or is contaminated, and the extra mass is not product.

Sources: OpenStax Chemistry 2e, section 4.4 “Reaction Yields” (limiting reactant, theoretical, actual and percent yield, Examples 4.12 and 4.13 and the practice problem for CF₂Cl₂). Related: stoichiometry calculator, limiting reactant calculator, grams to moles calculator and chemical equation balancer.