Percent Yield Calculator

Background.

Suppose you need 10 g of a product, and the step that makes it usually gives about 70%. You should plan the reaction around a theoretical yield of 10 ÷ 0.70 = 14.2857 g, and scale your limiting reactant to match. That is percent yield used in reverse, and it is how chemists size batches. Used forwards, it is the number at the bottom of every lab report: what share of the product the balanced equation allowed actually ended up in your vial.

The definition is simple. Percent yield = actual yield ÷ theoretical yield × 100. The actual yield is what you isolated and weighed. The theoretical yield is the maximum the balanced equation allows from the limiting reactant, a calculated figure that never comes off a balance. Both must be in the same unit, grams with grams or moles with moles, and the unit cancels. The calculator takes the theoretical yield as a given; if you have not worked it out yet, the theoretical yield and limiting reagent calculators will.

Real reactions fall short for four broad reasons: the reaction stops before all the limiting reactant is used up, some of it goes to side products, material is left behind on glassware, filters and in solution, and each purification step trades some product for a cleaner sample. Those losses compound across a synthesis. Ten steps at 80% each leave only 10.74% of the theoretical amount at the end, which is why multi-step routes are judged step by step.

A result above 100% is shown as calculated rather than cut off at 100. Conservation of mass rules it out for a pure, dry product, so the excess is a measurement telling you what else is in the solid, most often solvent or water. The reading that accompanies each result names the band it falls in and the usual explanations for it.

What is percent yield calculator?

Percent yield compares what a reaction delivered with what its stoichiometry allowed. The theoretical yield is calculated: moles of limiting reactant, times the mole ratio from the balanced equation, times the product's molar mass. The actual yield is measured: the mass, or amount in moles, of purified product you isolated. Their ratio, multiplied by 100, is the percent yield, a pure number with no units. It is a different quantity from conversion, the fraction of the limiting reactant that reacted at all, and from selectivity, the fraction of what reacted that became the product you wanted; for a single limiting reactant, yield equals conversion times selectivity. Nor does it measure waste. A reaction can give 99% of its theoretical product and still discard most of the reactants' atoms as by-products, which is what atom economy measures instead.

How to use this calculator.

1. 01Choose what to solve for. Leave it on percent yield if you know both amounts, or switch to actual yield or theoretical yield to work backwards from a known percentage.
2. 02Enter the actual yield: the mass of dried, purified product you weighed. A crude weight gives a crude yield, which is worth knowing but is not the figure to report.
3. 03Enter the theoretical yield in exactly the same unit. Nothing is converted for you, so milligrams against grams gives an answer off by a factor of 1,000.
4. 04When working backwards, enter the known percent yield as a percentage, 77.29 rather than 0.7729. The field you are solving for is ignored.
5. 05Read the percent yield together with the amount lost, which shows the missing material in your own unit and is often the more useful figure for deciding where it went.
6. 06Report the result to the significant figures your weighing supports, usually three for a balance reading to the milligram.

The formula.

The relation links three quantities, and any one can be found from the other two:

percent yield = actual ÷ theoretical × 100 actual = theoretical × percent ÷ 100 theoretical = actual ÷ (percent ÷ 100)

Whichever mode you choose, all five numeric results are returned, so a back-calculated theoretical yield comes with its amount lost and loss percentage too. The amount lost is theoretical − actual, in your unit, and the loss is 100 − percent yield, in percentage points. Both turn negative when the yield passes 100%, and the negative value is the excess mass in the sample.

The rules on zero follow from the division. A theoretical yield of zero cannot produce a percentage, so it is refused when solving for percent yield; a percent yield of zero cannot be divided into, so it is refused when solving for theoretical yield. An actual yield of zero is accepted and gives 0%, because a reaction that produced nothing is a real result. Negative amounts are refused everywhere.

The reading beside the result comes from fixed bands. Above 100% points to impurity or a wrong theoretical yield. Exactly 100% is labelled quantitative, with a prompt to confirm purity. From 95% upwards counts as very high; the Journal of Organic Chemistry's author guidelines, as cited here, single out yields above 95% for closer scrutiny of purity data, and that is the only band edge taken from a published source. From 70% to just under 95% is called good, with losses usually mechanical; 40% to under 70% moderate, pointing to side reactions or incomplete conversion; anything above zero but below 40% low; and zero is a failed run. The bands are a guide to where to look, not a grade.

Many bad percentages start upstream, in the theoretical yield. Choosing the wrong limiting reactant can only make it too large, since the true limiting reactant gives the smallest maximum, so that mistake pushes percent yields down, never above 100%. A theoretical yield that is too small usually comes from an unbalanced equation or the wrong form of the product: a salt that crystallises as a hydrate weighs more than its anhydrous formula, and a perfect run that isolates copper sulfate as its pentahydrate, measured against a theoretical yield for anhydrous CuSO4, would read 156.44%.

The arithmetic is exact, so the limit on precision is your measurements. A percent yield cannot be known better than the less precise of the two amounts behind it, and a theoretical yield rounded before entry carries that rounding into the answer.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Flowers, P., Theopold, K., Langley, R. & Robinson, W. R. (2019). Chemistry 2e, Section 4.4 'Reaction Yields'. OpenStax, Rice University. Peer-reviewed, openly licensed (CC BY 4.0). PRIMARY DEFINITION for this page: 'percent yield = (actual yield / theoretical yield) x 100 %', plus the definitions of limiting reactant, theoretical yield and actual yield, and Example 4.13 (CuSO4 + Zn -> Cu + ZnSO4; 1.274 g CuSO4, theoretical yield 0.5072 g Cu, 0.392 g isolated, 77.3 %) which is reproduced as this page's worked example. Retrieved 2026-07-29. Open access.
2. [2]American Chemical Society, The Journal of Organic Chemistry — Author Guidelines, section on reporting yields and purity of compounds. Requires that reported yields be weighed amounts of isolated and purified product, given as both weight and percentage rather than inferred from spectroscopic or chromatographic integration, and identifies yields above 95 % as warranting additional editorial scrutiny of purity documentation. Agrees with the OpenStax definition and supplies the reporting convention used by this page's interpretation bands. Retrieved 2026-07-29. Open access.
3. [3]Constable, D. J. C., Curzons, A. D. & Cunningham, V. L. (2002). 'Metrics to "green" chemistry — which are the best?' Green Chemistry 4(6), 521–527, doi:10.1039/B206169B. Royal Society of Chemistry, peer-reviewed. Table 1 reports measured yields and atom economies by reaction class across GlaxoSmithKline processes (for example: acid salt formation 83 % yield, hydrogenation 89 %, Grignard 71 %, resolution 36 %), which is the source for this page's statement about what yields are normal in industrial fine-chemicals practice. Retrieved 2026-07-29. Publisher page is paywalled; an author-accessible copy was consulted.
4. [4]Meija, J. et al. (2021). 'Atomic weights of the elements 2021 (IUPAC Technical Report)'. Pure and Applied Chemistry 93(5), 573–600, doi:10.1515/pac-2019-0603, as maintained in the CIAAW table 'Abridged Standard Atomic Weights 2024' (revision: 2024, based on the Atomic Weights 2021 report). Source of the molar masses used in the worked example: Cu 63.546, S 32.06, O 15.999, giving M(CuSO4) = 159.602 g/mol. Retrieved 2026-07-29. Open access.
5. [5]IUPAC (2007). Quantities, Units and Symbols in Physical Chemistry ('the Green Book'), 3rd edition, section 2.12 on chemical reactions — the formal basis for stoichiometric numbers and the extent of reaction that underlie any theoretical-yield calculation feeding this page. International Union of Pure and Applied Chemistry / RSC Publishing. Retrieved 2026-07-29. Bibliographic reference; the full text is a print/PDF edition rather than a live web page.
6. [6]Sheldon, R. A. (2018). 'Metrics of Green Chemistry and Sustainability: Past, Present, and Future'. ACS Sustainable Chemistry & Engineering 6(1), 32–48, doi:10.1021/acssuschemeng.7b03505. Peer-reviewed. Used here for the distinction this page draws between chemical yield and mass-efficiency metrics: Sheldon notes explicitly that chemical yield 'needed to be replaced or, at least, supplemented' by metrics that assign value to eliminating waste, which is why a high percent yield does not by itself mean an efficient reaction. Retrieved 2026-07-29. Publisher version paywalled; the author's institutional repository copy at TU Delft is open.