Percent Yield Calculator

At a glance:Percent yield is the core metric of reaction efficiency: it is the ratio of 'the amount of product actually recovered in the lab' to 'the maximum amount of product theoretically possible from the equation', expressed as a percentage: %yield = (actual yield ÷ theoretical yield) × 100%. The 'theoretical yield' is derived from stoichiometry: taking the limiting reagent, by the balanced equation's mole ratio, in an ideal world without side reactions or losses, the maximum product obtainable. The 'actual yield' is the mass (or moles) of product actually weighed after the experiment, including after purification. In reality the actual yield is almost always less than the theoretical yield, so percent yield is usually below 100%. Using this tool's default: a reaction theoretically yields 10 g but only 8 g is recovered, percent yield = 8 / 10 × 100% = 80% — meaning 80% of the theoretical product was obtained, a fairly good yield. Why is actual yield less than theoretical? There are several common reasons: (1) the reaction does not go to completion — an equilibrium reaction does not fully convert, or conditions (temperature, concentration) make the reaction slow, leaving unreacted starting material; (2) side reactions and competing reactions consume some raw material to make by-products; (3) mechanical loss during operation — some product left in the flask during transfer, filtration, washing, distillation, or stuck to glassware; (4) incomplete product separation or partial impurity dilution; (5) a tiny bit may also be lost to volatilisation or decomposition. Conversely, percent yield can exceed 100%, usually because the product is impure — not fully dried (water remains), or contains solvent or unreacted raw material, so the measured mass is inflated; a true yield above 100% means the product is impure and needs purification/redrying. Distinguish 'yield' from 'conversion' and 'selectivity': conversion = (reactant consumed / reactant fed) × 100% reflects raw-material utilisation; selectivity = (reactant that became the desired product / total reactant consumed) × 100% reflects side-reaction control; percent yield = conversion × selectivity (roughly), reflecting overall efficiency. In industry, raising percent yield directly lowers cost and waste, crucial for green chemistry. Uses: evaluating whether a synthesis experiment succeeded (commonly ≥ 70–80% good), comparing the merits of different routes, and diagnosing problems (low yield → incomplete reaction or large transfer loss). Notes: first, actual and theoretical yields must be the same physical quantity and same unit (both mass or both moles). Second, the theoretical yield needs the correct limiting reagent and mole ratio. Third, the theoretical yield must be > 0, otherwise division by zero. Fourth, percent yield > 100% usually signals impurity — check drying and purity.