Percent Yield CalculatorActual vs theoretical yield, with theoretical yield built in
Score your reaction in seconds, calculate the theoretical yield from your reactant, plan how much starting material you need, and see the overall yield of a multi-step synthesis.
By Manzoor Ahmad, pharmacist · Updated How do you calculate percent yield?
Percent yield = actual yield ÷ theoretical yield × 100. If 2.00 g of salicylic acid can make 2.609 g of aspirin in theory and you collect 2.17 g, the percent yield is 2.17 ÷ 2.609 × 100 = 83.2%. Use the same unit (grams or moles) for both yields.
Multi-step synthesis: overall yield
Enter the yield of each step. Overall yield multiplies, so it drops fast.
Percent yield and theoretical yield formulas
Here mr is the mass of the limiting reactant, Mr and Mp are the molar masses of reactant and product, and νr, νp are their coefficients in the balanced equation. If you are not sure which reactant limits the reaction, check with the limiting reactant calculator first.
How to use the percent yield calculator
- Percent yield: enter actual and theoretical yields in the same unit.
- From reactant: type the limiting reactant and product formulas, the mass of reactant used, the coefficients and your actual mass. The calculator finds the theoretical yield and the percent yield together.
- Plan a batch: enter the product you want and the yield you expect, and it tells you how much reactant to start with.
- Multi-step: add each step’s yield below the calculator to see the overall yield of a synthesis route.
Worked example: aspirin synthesis
Salicylic acid (C7H6O3) reacts with acetic anhydride to make aspirin (C9H8O4) in a 1:1 ratio. A student uses 2.00 g of salicylic acid and collects 2.17 g of dry aspirin.
- Molar masses: C7H6O3 = 138.122 g/mol; C9H8O4 = 180.159 g/mol.
- Moles of salicylic acid = 2.00 ÷ 138.122 = 0.01448 mol.
- Theoretical aspirin = 0.01448 mol × 1/1 × 180.159 = 2.609 g.
- Percent yield = 2.17 ÷ 2.609 × 100 = 83.2%, a good result for a teaching lab.
Aspirin synthesis is a classic because it connects lab chemistry to a medicine people know. In pharmaceutical manufacturing, yield is tracked at every step because lost product is lost cost.
What counts as a good percent yield?
| Yield range | Rating | Typical meaning |
|---|---|---|
| Over 100% | Check it | Wet or impure product, or a wrong theoretical yield |
| 90–100% | Excellent | Optimized or industrial-scale process |
| 70–90% | Good | Well-run lab reaction with careful work-up |
| 40–70% | Fair | Common in teaching labs and recrystallizations |
| Under 40% | Low | Incomplete reaction, side products or heavy losses |
These bands are practical guidance rather than a formal standard. Difficult reactions, such as new methods in research, may treat 30% as a success.
How quickly overall yield falls
| Yield per step | 3 steps | 5 steps | 10 steps |
|---|---|---|---|
| 95% | 85.7% | 77.4% | 59.9% |
| 90% | 72.9% | 59.0% | 34.9% |
| 80% | 51.2% | 32.8% | 10.7% |
| 70% | 34.3% | 16.8% | 2.8% |
Why yields fall short of 100%
Some reactions reach equilibrium or stop before all the limiting reactant is used.
Reactants form unwanted by-products instead of the target compound.
Product sticks to glassware, filter paper and spatulas.
Recrystallization trades yield for purity, since some product stays dissolved.
Percent yield FAQs
Percent yield = (actual yield ÷ theoretical yield) × 100. Both yields must be in the same unit, usually grams or moles.
Convert the limiting reactant's mass to moles, multiply by the mole ratio from the balanced equation, then multiply by the product's molar mass. For 2.00 g of salicylic acid making aspirin 1:1, theoretical yield = 2.00 ÷ 138.122 × 180.159 = 2.609 g.
It depends on the reaction. In teaching labs 60–85% is common. Industrial processes often aim for above 90%. In multi-step synthesis, 70–80% per step is generally considered good.
A yield over 100% usually means the product is still wet with solvent, contains impurities or side products, or was weighed with residue from the container. It can also mean the theoretical yield was calculated with the wrong limiting reactant.
Some product is lost during transfers, filtration and recrystallization, reactions may not go to completion, side reactions consume reactants, and some reactions reach equilibrium before all reactant is used.
Theoretical yield is the maximum product the balanced equation allows from the limiting reactant. Actual yield is what you really collect and weigh at the end of the experiment.
Yes. Percent yield is the same whether you use grams or moles, as long as actual and theoretical yields use the same unit.
Multiply the fractional yields of each step. Three steps at 85%, 72% and 90% give 0.85 × 0.72 × 0.90 = 55.1% overall.
Percent loss is 100% minus the percent yield. An 83% yield means 17% of the possible product was lost or never formed.
Divide the target mass by the expected fractional yield to get the required theoretical yield, then work back through the mole ratio and molar masses. The reverse planner in this calculator does it automatically.
No. Percent yield measures quantity, not purity. A sample can show a high yield while being impure, which is why yields are reported with a melting point, spectrum or other purity check.
Report percent yield to the same number of significant figures as your least precise measurement, usually three. 2.17 g ÷ 2.609 g × 100 is reported as 83.2%.
Sources
This percent yield calculator is for education and lab planning. Yield quality bands are practical guidance, not a regulatory standard.