Percent Yield Calculator
Enter any two of the three values (actual yield, theoretical yield, percent yield) and the calculator solves for the third. Switch the solve mode to work in either direction. Supports mass units from milligrams to kilograms and an optional moles mode when you know the molar mass of your product.
Formula
Worked example
You isolate 8.2 g of product but stoichiometry predicts 10 g: percent yield = (8.2 / 10) x 100 = 82.00%. Product lost = 10 - 8.2 = 1.8 g (18.00% loss). If the product has a molar mass of 18.015 g/mol, actual yield = 8.2 / 18.015 = 0.4552 mol.
How the Calculation Works
Percent yield compares what you actually made against the maximum the reaction could produce. Divide your measured actual yield by the theoretical yield predicted from the limiting reactant and the balanced equation, then multiply by 100. Because both masses share the same unit, the result is a dimensionless percentage that measures combined reaction and technique efficiency. This calculator can solve any of the three related quantities: given actual and theoretical yields it gives percent yield; given theoretical yield and percent yield it back-calculates the actual yield you should expect; and given actual yield and percent yield it finds the theoretical yield the calculation is based on.
Mass Units and Moles Mode
Actual and theoretical yields can be entered in milligrams, grams, or kilograms. The calculator converts everything to grams internally before computing the ratio, so you can mix units freely. If you turn on moles mode and supply the product molar mass, the calculator also divides each gram-mass by that molar mass to report the yields in moles, which is useful when comparing stoichiometric efficiency against the moles of limiting reactant you started with.
How to Use This Calculator
Select what you want to solve for from the Solve for dropdown. To find percent yield, enter the actual yield you weighed and the theoretical yield you calculated from stoichiometry. To back-calculate an actual yield (for example, to set a target or predict what a scaled-up batch should give), enter the theoretical yield and the percent yield. To find a theoretical yield when only the actual yield and efficiency are known, enter those two values. The result panel shows all three quantities, the mass lost, the percent loss, and optionally the mole quantities.
Percent Loss
Percent loss is the complement of percent yield: it is the fraction of the theoretical maximum that did not end up in your isolated product. Percent loss = (theoretical - actual) / theoretical x 100, which equals 100% minus the percent yield when the yield is at or below 100%. Knowing the percent loss is useful when writing up a synthesis, because it prompts you to account for where the missing material went: incomplete reaction, side products, or mechanical losses during workup.
What Affects Your Result
Real reactions rarely reach 100% yield. Incomplete reactions leave unreacted starting material, competing side reactions divert the limiting reactant into unwanted products, and equilibrium reactions stop before all reactant is consumed. Beyond chemistry, mechanical losses during filtration, transfer between vessels, recrystallization, and drying all reduce the final mass. Each handling step is an opportunity to lose product, which is why careful technique often matters as much as the reaction chemistry itself. Multi-step syntheses multiply the effect: a sequence of five steps each at 80% gives an overall yield of only 32.8%.
Limitations and Edge Cases
A percent yield above 100% is physically impossible for the desired product and signals a measurement problem. The usual culprits are residual solvent or water that was not fully removed during drying, or co-precipitated impurities adding extra mass. The calculator flags this condition but still shows the raw number so you can see how far off the result is. The result is only as good as your theoretical yield, so double-check the limiting reactant identification and the balanced equation before trusting a low yield number.
Yield quality scale
| Percent yield | Grade | Typical context |
|---|---|---|
| >= 90% | Excellent | Well-optimised reactions, industrial processes |
| 80-89% | Very good | Good lab technique, simple purification |
| 70-79% | Good | Acceptable for most teaching and research labs |
| 50-69% | Fair | Equilibrium-limited or multi-step with losses |
| 40-49% | Low | Difficult chemistry or significant mechanical loss |
| < 40% | Poor | Needs optimisation of conditions or workup |
| > 100% | Error | Impurity, solvent, or weighing error |
General benchmarks used in synthetic chemistry. The acceptable threshold depends heavily on the reaction type, number of steps, and how difficult the purification is.
Frequently asked questions
What is a good percent yield?
It depends on the reaction type. Simple, well-optimised reactions can exceed 90%, while multi-step syntheses, equilibrium reactions, or reactions with difficult purifications may be considered successful at 50-70%. A general rule of thumb: >= 90% is excellent, 80-89% is very good, 70-79% is good, 50-69% is fair, and below 50% warrants investigation. There is no universal threshold as yields are judged relative to what is typical for that particular transformation.
Why is my percent yield over 100%?
A yield above 100% means your measured product weighs more than the reaction could possibly produce, so the extra mass is not product. The most common causes are incomplete drying that leaves trapped solvent or water, or impurities that co-precipitate with your product. Dry the sample to a constant mass (weigh, dry more, weigh again until no change) and re-weigh. The yield should fall below 100%.
How do I find the theoretical yield?
Identify the limiting reactant, convert its mass to moles by dividing by its molar mass, use the mole ratio from the balanced equation to find moles of product, then multiply by the product molar mass to get the maximum possible mass. That maximum is the theoretical yield you enter into this calculator. You can also use the reverse mode here: if you know the actual yield and an expected efficiency from a literature source, the calculator will back out the implied theoretical yield.
How do I calculate actual yield from percent yield?
Rearrange the formula: actual yield = (percent yield / 100) x theoretical yield. For example, if the theoretical yield is 10 g and you expect 82% efficiency, the actual yield = (82 / 100) x 10 = 8.2 g. Switch the Solve for dropdown to "Actual yield" and this calculator does the algebra for you.
How do I convert yield from grams to moles?
Divide the mass in grams by the molar mass of the product in g/mol. For example, 8.2 g of water (molar mass 18.015 g/mol) = 8.2 / 18.015 = 0.4552 mol. Turn on the moles mode toggle and enter the molar mass; the calculator handles the conversion automatically for both actual and theoretical yields.
What is percent loss and how is it related to percent yield?
Percent loss = (mass lost / theoretical yield) x 100, where mass lost = theoretical - actual (or 0 if actual exceeds theoretical). It is the exact complement of percent yield when yield <= 100%, so percent yield + percent loss = 100%. Tracking the loss helps you identify where product is going during workup and purification.