Last updated: June 2026
Use this percentage yield calculator to compare the amount of product actually obtained with the maximum theoretical amount expected from a reaction. It can also rearrange the percentage yield formula to calculate actual yield or theoretical yield.
- Enter any two of the three values: actual yield, theoretical yield and percentage yield.
- Leave the value you want to calculate completely blank.
- Use the same unit for actual yield and theoretical yield.
- Select the unit from the dropdown so it is displayed clearly in the answer.
- Select Calculate to see the rearranged formula, substitution and result.
What is percentage yield?
Percentage yield compares the amount of product obtained in a real experiment with the maximum amount predicted by stoichiometric calculations.
The actual yield is the amount of product collected experimentally. The theoretical yield is the maximum possible amount calculated from the limiting reagent and the balanced equation.
Real yields are often below the theoretical maximum because reactions may be incomplete, product may be lost during separation or purification, and side reactions may produce unwanted substances.
Percentage yield formula
The actual yield and theoretical yield must use the same unit. For example, both values may be in grams or both may be in moles.
Actual yield and theoretical yield
Actual yield is measured after the reaction and product-isolation process. It is the real quantity of product obtained.
Theoretical yield is calculated before comparison with the experiment. It is determined from the limiting reagent and the mole ratio in the balanced equation.
When percentage yield and theoretical yield are known, actual yield can be calculated:
When actual yield and percentage yield are known, theoretical yield can be calculated:
Worked examples
Example 1: Calculating percentage yield
A reaction has a theoretical yield of 10.0 g. The experiment produces 8.20 g.
The experiment therefore produced 82.0% of the maximum possible product.
Example 2: Calculating actual yield
A reaction has a theoretical yield of 12.5 g and a percentage yield of 76.0%.
Example 3: Calculating theoretical yield
A student obtains 6.00 g of product at a percentage yield of 75.0%.
Why percentage yield is often less than 100%
Product can be lost during filtration, washing, drying, crystallisation or transfer between containers. Some reactants may not react completely, and competing reactions may form other products.
In reversible reactions, equilibrium may be reached before all reactants are converted into products. This also reduces the amount of desired product formed.
Can percentage yield be more than 100%?
The true yield should not exceed 100% because theoretical yield represents the maximum amount of pure product possible from the limiting reagent.
A calculated value above 100% usually indicates that the collected product is wet, impure or contaminated, or that one of the measurements or calculations is incorrect.
Common exam traps
Frequently Asked Questions
What does a percentage yield calculator calculate?
It calculates percentage yield, actual yield or theoretical yield when the other two values are known.
What is the formula for percentage yield?
Percentage yield equals actual yield divided by theoretical yield, multiplied by 100%.
What is the difference between actual yield and theoretical yield?
Actual yield is obtained experimentally. Theoretical yield is the maximum amount predicted from the limiting reagent and balanced equation.
Why is percentage yield usually below 100%?
Reactions may be incomplete, product may be lost, side reactions may occur, or purification may not recover all the product.
Why might percentage yield be above 100%?
The measured product may contain water, solvent or impurities, causing its recorded mass to be too high.