The formula
r = (mᵣ / mₜ) × 100
| Symbol | Quantity | Unit |
|---|---|---|
| r | Yield | % |
| mᵣ | Actual yield | g |
| mₜ | Theoretical yield | g |
What it means
Stoichiometry says how much product should come out if all the limiting reagent converted and nothing was lost. In a real laboratory that never happens: some stays in the flask, some reacts down another path, some is lost in filtering. Yield measures that gap between the theory and the balance, and it is one of the few figures in chemistry you learn by looking at what went wrong.
How to work it out by hand
- Work out the theoretical yield from the limiting reagent
- Weigh the product you obtained and purified
- Divide what you got by the theoretical amount
- Multiply by a hundred
What is worth knowing
A yield above a hundred per cent does not mean the reaction went better than possible: it means the product is wet or carries impurities. It is the classic sign that the sample needs drying, and it should be treated as a measurement error rather than a result. In multi-step organic synthesis, yields also multiply: five steps at 80 % give 33 % overall, not 80 %. That product is what makes a long route unviable even when every stage looks reasonable on its own.