Percent Yield Calculator
Reaction efficiency from actual and theoretical yields, with loss and verdict.
What it does
Percent yield grades a reaction: what the flask kept against what stoichiometry promised. Side reactions, transfers, and purification each take a cut, so real yields land under the theoretical ceiling.
The tool above takes actual yield with theoretical yield in matching units. It returns the percent with the lost amount and a plain verdict beside them.
The default of 14.9 g kept from 15.7 g possible gives 94.9%: excellent. A zinc run keeping 65.2 g of 88.3 g possible gives 73.8%: good bench work.
The definition follows open chemistry textbook stoichiometry chapters with matching worked examples. Both cap proper yields at 100% and treat anything above as measurement error.
How to use
- Enter the actual isolated product in any unit.
- Enter the theoretical maximum in the same unit.
- Read percent first for the efficiency grade.
- Read loss for how much slipped away.
- Read the verdict before scaling the reaction up.
Formula
- actual
- Product actually isolated and weighed.
- theoretical
- Stoichiometry maximum from the limiting reactant.
- 100%
- Ceiling: proper yields never pass it.
Units cancel, so grams, moles, or liters all work when matched. Find theoretical yield first from the balanced equation through the limiting reactant, as the limiting page shows.
Worked example
Example: 14.9 g of 15.7 g possible
Defaults: actual 14.9, theoretical 15.7.
- Ratio: 14.9 / 15.7 = 0.94904.
- Percent: 0.94904 x 100 = 94.9%.
- Loss: 15.7 - 14.9 = 0.8 units.
- Verdict: 90 and above reads Excellent.
- Tool shows 94.9 %, 0.8 units lost, Excellent.
Reference table
| Actual / theoretical | Yield | Verdict |
|---|---|---|
| 14.9 / 15.7 | 94.9 % | Excellent |
| 45 / 50 | 90.0 % | Excellent |
| 65.2 / 88.3 | 73.8 % | Good |
| 30 / 60 | 50.0 % | Fair |
Limits
- Efficiency only; purity needs analysis of its own.
- Theoretical must come from balanced stoichiometry first.
- Multi step routes multiply step yields, shrinking fast.
- Hazard and cost scale with scale-up beyond the percent.
Common mistakes
- Mixing grams with moles across the fraction.
- Using an excess reactant for the theoretical.
- Celebrating over 100% instead of reweighing.
- Weighing wet product as dry yield.
- Skipping the limiting reactant check first.
Try it yourself
Quick checks. Answers sit tucked under each question.
65.2 g of 88.3 g possible?
73.8% with 23.1 lost: Good.
Yield above 100%?
Measurement error flag: recheck weights and dryness.
Grams versus moles?
Either, matched top and bottom: the units cancel.
Questions
What is percent yield?
Actual over theoretical times 100: the kept share of the possible.
What is theoretical yield?
The stoichiometry maximum from the limiting reactant via the balanced equation.
Can yield pass 100%?
No. Wet product, impurities, or math errors explain every case above it.
What is a good percent yield?
90 plus excellent, 70s good, 50s fair: context and step count decide.
Why is actual lower?
Side reactions, incomplete conversion, transfers, and purification losses.
Multi step yields?
Multiply step percents: 70% x 40% x 72% x 35% leaves 7.5% overall.