The one calculation, and where the two numbers come from
Theoretical yield is the most product the reaction could make from your limiting reactant, worked out from the balanced equation. Actual yield is what you actually weighed out after the reaction. Both must be in the same unit — grams or moles — before you divide.
Reading the result
| Percent yield | Rating |
|---|---|
| 90–100% | Excellent |
| 80–90% | Very good |
| 70–80% | Good |
| 50–70% | Fair |
| Below 50% | Poor |
Typical ranges by reaction type: esterifications and simple organic condensations often land at 80–95%, halogenations near 85–98%, and complex pharmaceutical routes anywhere from 40 to 90% per step.
Why yield almost never hits 100%, and why it matters at scale
- Incomplete reaction. Many reactions sit at equilibrium, so not every bit of reactant becomes product.
- Side reactions. Some reactant is diverted into unwanted by-products.
- Losses in workup. Product is left behind during filtering, drying, extraction and transfers.
- Multi-step penalty. Yields multiply across steps. Ten steps at 80% each give an overall 0.810 ≈ 11%, which is why long syntheses guard every percent.
Common questions
Can percent yield be more than 100%?
Not in a clean experiment. A value above 100% almost always means the product was still wet with solvent, was contaminated, or the theoretical yield was miscalculated. Dry and reweigh before trusting the number.
What counts as a good percent yield?
As a rough scale: 90% or more is excellent, 80 to 90% is very good, 70 to 80% is good, and below 50% is poor. Multi-step and pharmaceutical syntheses often accept much lower because losses compound at every stage.
Do actual and theoretical yield have to be in the same unit?
Yes. Put both in grams, or both in moles, before you divide. Mixing a mass with a mole count gives a meaningless ratio.
