Percent Yield Calculator
Compare what a reaction actually produced against what it should have produced. Solve for percent yield, actual yield, or theoretical yield.
The formula
Percent yield = (actual yield ÷ theoretical yield) × 100
Two numbers go into it, and they mean quite different things.
The theoretical yield is a prediction. It comes from stoichiometry: you take the amount of limiting reactant, apply the mole ratio from the balanced equation, and convert to grams. It assumes every particle reacts and nothing goes missing.
The actual yield is a measurement. You isolate the product, dry it, and weigh it. That number comes off a balance, not out of a calculation.
Because the units cancel, both values simply need to be in the same unit. Grams and grams, or moles and moles, both work.
Worked example
A reaction should produce 12.5 g of product. After filtering and drying, you weigh 9.8 g. What is the percent yield?
Percent yield = (9.8 ÷ 12.5) × 100 = 78.4%
Turned around, if you know a preparation typically runs at 78% and you need 20 g of product, you should plan to start with enough reactant for about 26 g.
Where the missing product goes
A yield below 100% is normal, and the reasons are physical rather than mysterious.
- Transfer losses. Product clings to the beaker, the stirring rod, and the filter paper.
- Solubility. Some product stays dissolved in the liquid you pour away.
- Side reactions. Reactants take a different path and make something else.
- Incomplete reaction. Reversible reactions settle at equilibrium before all the reactant is used up.
- Impure reactants. If the starting material is 95% pure, the ceiling is already below 100%.
- Losses during purification. Recrystallizing improves purity but always sacrifices some mass.
What counts as a good yield
| Percent yield | Usually described as |
|---|---|
| Above 90% | Excellent |
| 70 to 90% | Good, typical of a well-run school preparation |
| 40 to 70% | Moderate, common in multi-step organic synthesis |
| Below 40% | Poor, worth investigating |
Context matters more than the number. A 50% yield on a difficult synthesis can be a strong result, while 90% on a simple precipitation might be disappointing. In a multi-step synthesis the yields multiply, so five steps at 80% each leave you with only 33% overall.
Yields above 100 percent
A percent yield over 100 is not possible in reality, because mass is conserved. If you calculate one, something in the measurement is wrong. The usual causes are:
- The product is still damp, so you weighed solvent along with it.
- Unreacted starting material or a byproduct is mixed in.
- The theoretical yield was worked out from the wrong limiting reactant.
- The equation used for the calculation was not balanced.
The fix is usually to dry the sample to constant mass. Weigh it, dry it further, and weigh again. When the reading stops changing, the solvent has gone.
Percent yield, percent error, and atom economy
| Measure | Answers |
|---|---|
| Percent yield | How much of the possible product did I recover? |
| Percent error | How far is my measurement from the accepted value? |
| Atom economy | How much of the reactant mass ends up in the product I want? |
Atom economy is a design question rather than a laboratory one. A reaction can have a 100% yield and still have poor atom economy, if most of the reactant mass leaves as byproducts. Green chemistry pays close attention to both.
Frequently asked questions
What is the percent yield formula?
Percent yield equals the actual yield divided by the theoretical yield, multiplied by 100. Both yields must be in the same unit, usually grams.
How do I find the theoretical yield?
Work out which reactant is limiting, convert it to moles, multiply by the mole ratio from the balanced equation, then multiply by the molar mass of the product. Our stoichiometry calculator does all three steps.
Why is my percent yield over 100?
It means the measurement is off rather than the chemistry. Usually the product has not been dried fully, so you weighed trapped solvent too, or an impurity is mixed in. Dry the sample to constant mass and weigh again.
What is a good percent yield?
It depends on the reaction. Above 90 percent is excellent, and 70 to 90 percent is typical for a straightforward preparation. Complex organic syntheses often run at 40 to 70 percent per step and that can still be a strong result.
Is percent yield the same as percent error?
No. Percent yield compares how much product you recovered with how much was possible. Percent error compares a measured value with an accepted or true value.
Can percent yield be calculated in moles?
Yes. The units cancel in the division, so as long as the actual and theoretical yields are both in moles, or both in grams, the percentage comes out the same.
Related terms
Next: work out the theoretical yield itself on the stoichiometry calculator.