Case 1
- Actual yield (g)
- 8.5g
- Theoretical yield (g)
- 10g
85.00%
Open with these valuesPercent Yield Calculator
85.00%
Result: 85.00 %Divide what you actually recovered by the maximum the stoichiometry allows and multiply by 100: 8.5 g out of a possible 10 g is 85 %. Keep both amounts in the same unit so they cancel. A figure above 100 % is arithmetic, not chemistry — usually wet or impure product.
Worked examples
Case 2
- Actual yield (g)
- 15.2g
- Theoretical yield (g)
- 20g
76.00%
Open with these valuesCase 3
- Actual yield (g)
- 12g
- Theoretical yield (g)
- 10g
120.00%
Open with these valuesHow it's calculated
percent yield = (actual ÷ theoretical) × 100
- StepWork out the theoretical yield from the limiting reactant.
- StepWeigh the dry, purified product you actually recovered.
- ResultDivide the second by the first and multiply by 100.
What this number means
Actual over theoretical, not one measurement
The denominator is the most the reaction could give, worked out from the limiting reactant by stoichiometry. The numerator is the dry, purified product you really recovered.
Above 100 % is arithmetic, not chemistry
12 g out of a possible 10 g gives 120 %, and the calculator shows it rather than hiding it. A figure that high nearly always means wet or impure product, or a miscalculated theoretical yield.
Both amounts need the same unit
Grams and grams, or moles and moles — being a ratio, the unit cancels and mixing them gives a meaningless number. Scale drops out too: 8.5 out of 10 and 0.85 out of 1 both come to 85 %.
Below 100 % is the normal case
Side products form, equilibria never convert fully, and material stays behind on glassware and during recrystallisation. For a multi-step synthesis 70–90 % is often considered good.
Commonly misread
A yield above 100 % means the reaction did better than expected.
Chemistry does not allow it. The product is nearly always still wet with solvent or contaminated, or the theoretical yield was worked out wrongly.
Grams in the numerator and moles in the denominator are fine.
Only matching units cancel out of the ratio. Mixed ones leave a number that means nothing.
A yield below 100 % means something went wrong in the flask.
Real reactions lose product at every step, so 70–90 % is often considered good for a multi-step synthesis.
Weigh the product straight after the reaction.
Weigh it dry and purified. Residual solvent pushes the figure up and is the usual reason a yield reads above 100 %.
Reference table
| Actual, theoretical | What that run looked like | Percent yield |
|---|---|---|
| 0, 10 | nothing recovered | 0.00 |
| 15.2, 20 | a lossy multi-step synthesis | 76.00 |
| 8.5, 10 | a good ordinary run | 85.00 |
| 0.85, 1 | the same ratio on a smaller scale | 85.00 |
| 9, 10 | a clean reaction | 90.00 |
| 12, 10 | impossible — check for solvent or impurities | 120.00 |
Questions
How do I calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. Recovering 8.5 g when the maximum was 10 g gives 85 %.
What is the difference between actual and theoretical yield?
The theoretical yield is the most the reaction could give, worked out from the limiting reactant by stoichiometry. The actual yield is what you really recovered, and it is almost always lower because of side reactions and losses on glassware and filters.
Can the percent yield be over 100 %?
The arithmetic will show it, but chemistry will not. A figure above 100 % nearly always means the product is still wet with solvent, contains impurities, or the theoretical yield was miscalculated.
Why is the yield usually below 100 %?
Real reactions lose product at every step: side products form, equilibria never convert fully, and material stays behind on glassware and during recrystallisation. For a multi-step synthesis 70–90 % is often considered good.
Which units should I use?
The same one for both — grams and grams, or moles and moles. Because it is a ratio the units cancel, and mixing them gives a meaningless number.
Sources and last check
Information, not professional advice.