Percent Yield Calculator
Calculate the percent yield of a chemical reaction from actual and theoretical yields.
Understand why reactions never give 100% yield.
Percent yield compares how much product you actually obtained to the maximum theoretically possible.
Formula:
% yield = (actual yield / theoretical yield) × 100
Theoretical yield is the maximum amount of product calculated from stoichiometry, assuming the limiting reagent is completely consumed and no product is lost.
Actual yield is what you physically collect after the reaction and purification.
Why is percent yield always ≤ 100%? Real reactions rarely produce 100% yield due to:
- Incomplete reaction: Equilibrium limits products formed
- Side reactions: Other products form alongside the desired product
- Product loss: During transfer, filtration, crystallization, or distillation
- Impure reagents: Contaminated starting materials
- Measurement errors: Losses during weighing or handling
Typical yield ranges in different fields:
| Context | Typical % Yield |
|---|---|
| Industrial chemical synthesis | 85–95% (optimized processes) |
| Multi-step pharmaceutical synthesis | Often 40–60% per step |
| Organic chemistry lab (first attempt) | 40–80% |
| Biological systems (ATP synthesis) | ~40% efficiency |
| Combustion engine | 15–40% mechanical efficiency |
Atom economy (related concept):
Even with 100% yield, a reaction may waste atoms if large byproducts are formed.
Atom economy = MW of desired product / sum of MW of all products × 100
For green chemistry, high atom economy is just as important as high percent yield.