Percent Yield Calculator

Percent yield compares what a reaction really made with the most it could make: percent yield = actual yield ÷ theoretical yield × 100. If a reaction could make 20.0 g but you collect 17.5 g, the percent yield is 87.5%.

How to use the calculator

1. Choose what you want to find: the percent yield, the actual yield or the theoretical yield.
2. Enter the other two values. Use the same unit (grams, or moles) for both yields.
3. Press Calculate and open Show steps to see the formula with your numbers.

Percent yield formula

• Percent yield = actual yield ÷ theoretical yield × 100
• Actual yield = theoretical yield × percent yield ÷ 100
• Theoretical yield = actual yield ÷ (percent yield ÷ 100)

The actual yield is what you measure in the lab. The theoretical yield comes from stoichiometry: the amount of product the limiting reactant can make if every bit of it reacts.

Worked example

Heating 10.0 g of calcium carbonate (CaCO₃, 100.09 g/mol) gives calcium oxide (CaO, 56.08 g/mol): CaCO₃ → CaO + CO₂.

1. Moles of CaCO₃ = 10.0 ÷ 100.09 = 0.0999 mol.
2. The ratio is 1 : 1, so at most 0.0999 mol of CaO forms.
3. Theoretical yield = 0.0999 × 56.08 = 5.60 g.
4. If you collect 5.04 g, the percent yield = 5.04 ÷ 5.60 × 100 = 90.0%.

Why yields are below 100%

• Some product sticks to glassware or is lost when filtering and moving it.
• Side reactions turn some reactant into other products.
• Reversible reactions stop at equilibrium before all the reactant is used.

A result above 100% is a warning sign: the product may still contain water or solvent, or have impurities in it.

Percent yield practice questions

Test yourself with 6 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do you calculate percent yield?

Divide the actual yield by the theoretical yield and multiply by 100. 17.5 g ÷ 20.0 g × 100 = 87.5%.

How do you find the theoretical yield?

Convert the limiting reactant to moles, use the mole ratio from the balanced equation to get moles of product, then multiply by the product's molar mass.

Can percent yield be over 100%?

Not for a pure, dry product. A yield above 100% points to water, solvent or other impurities in the product, or a mistake in the theoretical yield.

What is a good percent yield?

It depends on the reaction. Simple one-step reactions often reach 80 to 95%, while reactions with many steps can have much lower overall yields because the losses multiply.

Sources

• LibreTexts Chemistry: Theoretical yield and percent yield
• IUPAC Gold Book: yield

Related calculators

• Limiting Reagent Calculator
• Molar Mass Calculator
• Percent Error Calculator
• Percentage Calculator

Browse all calculators