What this calculator does
Percent yield is what you actually got divided by what the stoichiometry says you should have got. Recovering 8.5 g where the theory predicts 10 g is an 85% yield.
Yields below 100% are the norm, and there are several reasons that have nothing to do with the chemistry failing: product left in the flask, losses during filtration and transfer, incomplete reaction, competing side reactions, and material lost in purification. A yield above 100% is not a triumph but a signal that the product is wet or impure.
The formula
The actual yield is divided by the theoretical yield and multiplied by 100. The theoretical yield comes from the limiting reagent and the reaction stoichiometry, and getting that wrong is the more common source of error. The mass lost is reported alongside, which is often more informative when diagnosing where a preparation went wrong.
| Term | Meaning |
|---|---|
| Theoretical yield | The maximum product possible from the limiting reagent, by stoichiometry. |
| Actual yield | What was isolated and weighed. |
| Limiting reagent | The reactant that runs out first, which sets the theoretical yield. |
| Atom economy | A different measure, concerning how much of the reactant mass ends up in the desired product by design. |
The inputs explained
| Field | What to enter |
|---|---|
| Actual yield (g) | Actual yield: the mass of purified product obtained. |
| Theoretical yield (g) | Theoretical yield: the maximum from the limiting reagent. Calculate this from the balanced equation. |
When to use it
Reporting a synthesis
Percent yield is the standard figure quoted for any preparative reaction.
Comparing methods
Two routes to the same product are compared partly on yield, alongside cost and difficulty.
Diagnosing a poor result
A low yield prompts questions about which step lost material, and how much.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What does each recovery give?
A range of actual yields against the same theoretical maximum.
| Actual yield | Percent yield | Product lost | Theoretical yield |
|---|---|---|---|
| 5 g | 50.0% | 5.000 g | 10.000 g |
| 7.5 g | 75.0% | 2.500 g | 10.000 g |
| 8.5 g | 85.0% | 1.500 g | 10.000 g |
| 10 g | 100.0% | 0.000 g | 10.000 g |
Questions
Why is my yield below 100%?
Almost always a combination of mechanical losses during transfer and filtration, incomplete reaction, side reactions consuming reactant, and material lost in recrystallisation or chromatography. Yields of 70 to 90% are normal for a well-behaved preparation.
Can percent yield exceed 100%?
Not genuinely. A figure above 100% means the product is contaminated, most often with residual solvent or water. Dry the sample to constant weight and re-weigh. If it persists, the product contains an impurity and needs further purification.
How do I find the theoretical yield?
Identify the limiting reagent by converting each reactant mass to moles and dividing by its stoichiometric coefficient. The smallest result is limiting. Multiply its moles by the product coefficient and the product molar mass. Errors here are more common than errors in the yield calculation itself.
What is the difference between percent yield and atom economy?
Percent yield measures how well a specific run performed against its own theoretical maximum. Atom economy measures how much of the reactant mass the reaction is capable of placing in the desired product by design. A reaction can have 100% yield and poor atom economy.
For the theoretical maximum, see the theoretical yield calculator. For the efficiency of the reaction design, see the atom economy calculator.