Percent Yield Calculator
Divide what you actually got by what the equation says you should have got. Works in grams or moles, as long as both match.
Actual yield against theoretical yield
Product not recovered
1.5
Loss as a percentage
15%
Percent yield
85%
8.5 ÷ 10 × 100
The percent yield formula
Percent yield = Actual yield ÷ Theoretical yield × 100
Both yields must be in the same unit. Grams over grams, or moles over moles. Mixing the two is the most common source of a wrong answer, and the units do not cancel to warn you.
Worked example — you isolated 8.5 g, the equation predicts 10 g
8.5 ÷ 10 = 0.85
0.85 × 100 = 85
So the percent yield is 85%.
Finding the theoretical yield
- Balance the equation.
- Work out which reagent is limiting — convert each starting mass to moles and divide by its coefficient. The smallest result is the limiting reagent.
- Apply the mole ratio to get moles of product.
- Multiply by the product's molar mass to get grams.
Step 2 is where most errors happen. Using the wrong limiting reagent gives a theoretical yield that is too high or too low, and the percent yield inherits the mistake without any sign that something is wrong.
A yield above 100% means something went wrong
You cannot make more product than the atoms allow. A figure over 100% always points at one of these:
- The sample is wet. Residual solvent adds mass. Dry to constant weight and reweigh.
- The product is impure. Unreacted starting material or by-product is being weighed as product.
- The theoretical yield is wrong. Usually the wrong limiting reagent, or an unbalanced equation.
Why yields are never 100%
- Product is lost on filter paper and glassware at every transfer.
- Some reactions reach equilibrium before going to completion.
- Side reactions consume starting material.
- Purification removes product along with the impurities.
In a multi-step synthesis the yields multiply. Four steps at 80% each give 0.8⁴ = 41% overall, which is why long routes are judged on the overall figure rather than on any single step.
Common questions
- What is the percent yield formula?
- Percent yield = actual yield ÷ theoretical yield × 100. Both yields must be in the same unit, either grams or moles.
- Can percent yield be over 100%?
- Not chemically. A figure above 100% means the product is still wet with solvent, contains unreacted starting material, or the theoretical yield was calculated wrongly. Dry the sample and check the limiting reagent.
- How do I find the theoretical yield?
- Identify the limiting reagent, convert its mass to moles, apply the mole ratio from the balanced equation, then convert back to the mass of product.
- What counts as a good percent yield?
- It depends on the reaction. Above 90% is excellent for a simple synthesis. A multi-step route can be considered successful at well under 50%, because each step multiplies.