About the Percent Yield Calculator
This percent yield calculator tells you how efficient a chemical reaction was. Enter the actual yield you collected and the theoretical yield predicted by stoichiometry, and it returns the percentage yield, the amount of product lost and the fraction recovered. It can also work backwards: find the actual yield you should expect from a known percent yield, or the theoretical yield implied by a measured product mass.
It is aimed at chemistry students writing up lab reports, teachers setting problems and anyone scaling up a synthesis who needs to plan how much starting material to use. Masses can be in any unit — grams, milligrams, kilograms — or you can use moles, as long as actual and theoretical yield are in the same unit.
If you still need the theoretical yield, work it out first from the limiting reactant and the balanced equation (see the theoretical yield and limiting reactant calculators). A percent yield above 100% usually means the product is wet or impure rather than that extra product formed.
With the default inputs, the percent yield is 85%. Change any value above to recalculate instantly.
How to use the percent yield calculator
- 1Choose whether to solve for percent, actual or theoretical yield.
- 2Pick the unit you are using for both yields.
- 3Enter the two known values.
- 4Read the result, the amount lost and the assessment of how efficient the reaction was.
Formula and method
Percent yield compares the amount of product you actually obtained with the maximum amount the balanced equation says is possible from the limiting reactant. Dividing actual by theoretical yield and multiplying by 100 gives the percentage.
Rearranging the same equation gives actual yield = theoretical × percent ÷ 100 and theoretical yield = actual × 100 ÷ percent. Both yields must use the same unit — grams, milligrams, kilograms or moles — because the units cancel. The lost amount is simply the difference between theoretical and actual yield. If the actual yield exceeds the theoretical yield, no product was "lost"; the calculator instead shows the excess mass, which is usually trapped solvent, water or impurities.
- Actual yield
- Amount of product measured after the experiment
- Theoretical yield
- Maximum product predicted by stoichiometry from the limiting reactant
Worked examples
Typical lab synthesis
Collecting 8.5 g when 10 g was possible gives 8.5 ÷ 10 × 100 = 85% yield; 1.5 g was lost along the way.
Aspirin synthesis
If salicylic acid should give 2.61 g of aspirin and you recover 2.10 g, the yield is 2.10 ÷ 2.61 × 100 ≈ 80.46%.
Planning an industrial batch
A process with a proven 92% yield and 250 kg theoretical output should deliver 250 × 0.92 = 230 kg of product.
Theoretical yield from a known percent
If 12 g represents a 75% yield, the theoretical maximum was 12 × 100 ÷ 75 = 16 g.
Wet product above 100%
5.4 ÷ 5.0 × 100 = 108%. Nothing was lost; the extra 0.4 g is almost certainly water, solvent or impurity, so the product should be dried and re-weighed.
Frequently asked questions
How do you calculate percent yield?+
Divide the actual yield by the theoretical yield and multiply by 100. For example, 4.2 g obtained from a theoretical 5.0 g is 4.2 ÷ 5.0 × 100 = 84% yield. Both values must be in the same unit.
What is the difference between actual and theoretical yield?+
Theoretical yield is the maximum product calculated from the balanced equation and the limiting reactant. Actual yield is what you measure in the lab, which is almost always lower.
Why is percent yield less than 100%?+
Common reasons include incomplete reactions, reversible equilibria, side reactions producing other products, and physical losses during filtration, transfers and recrystallisation.
Can percent yield be over 100%?+
Not for a pure, dry product. A value above 100% usually means the product still contains solvent or water, or is contaminated with impurities or unreacted starting material.
What is a good percent yield?+
It depends on the reaction, but in teaching labs yields above 70% are generally considered good and above 90% excellent. Multi-step syntheses multiply losses, so overall yields are often much lower.