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Science

Percent Yield Calculator (Chemistry)

Percent yield measures how much product you actually isolated relative to the theoretical maximum the balanced equation predicts — a core metric for undergraduate organic-chemistry labs, synthesis reports and pharma process chemistry. Enter actual and theoretical masses for an instant percentage, or derive the theoretical mass from limiting-reagent moles, stoichiometric ratio and product molar mass.

Input method

Percent yield

75.0%

< 40% 40–70% 70–90% ≥ 90%

Formula: % yield = (actual ÷ theoretical) × 100

Formula

% yield = (actual ÷ theoretical) × 100; theoretical mass = (mol of limiting reagent) × (stoichiometric ratio) × (product molar mass)

Frequently asked

How do I calculate the theoretical yield?

Start with the balanced equation. Identify the limiting reagent by dividing each reactant's moles (mass ÷ molar mass) by its coefficient — the smallest quotient wins. Then theoretical moles of product = (moles of limiting reagent) × (product coefficient ÷ limiting-reagent coefficient), and theoretical mass = moles × product molar mass. The "from moles" mode in this tool does the last two steps for you: enter limiting-reagent moles, stoichiometric ratio and product molar mass.

Why does my yield calculation exceed 100 %?

Mass conservation means a true yield can never exceed 100 %. Common causes: (1) the product is not fully dry and still contains solvent or water; (2) the product contains starting material, by-product or other impurities; (3) the filter paper or weighing vessel was included in the mass; (4) the theoretical yield was computed incorrectly — wrong limiting reagent or wrong stoichiometric ratio; (5) balance is uncalibrated. Fixes: dry under high vacuum (or over P₂O₅), confirm purity by NMR or TLC, then reweigh. If still > 100 %, recheck the theoretical calculation.

What counts as a "good" yield?

There is no single threshold — it depends on the reaction type and number of steps. Simple substitutions, acid-base neutralisations, and recrystallisations can routinely exceed 90 %; multi-step organic synthesis typically gives 60–80 % per step; transition-metal catalysis, stereoselective reactions and transformations on sensitive functional groups can be 30–50 %. Industrial process chemistry demands much higher (often ≥ 85 %) to control cost and waste. The < 40 / 40–70 / 70–90 / ≥ 90 bands here are an undergraduate teaching guide; research reports should benchmark against literature yields under similar conditions rather than absolute numbers.

How do I compute the overall yield of a multi-step synthesis?

Multiply the individual step yields in decimal form. For example, step A 90 %, B 75 %, C 60 % gives overall = 0.90 × 0.75 × 0.60 = 0.405 = 40.5 %. The takeaway is that even moderate per-step yields compound quickly, so chemists value "step economy" (fewer steps) and front-load the lowest-yielding step early in the route. In retrosynthetic planning, putting the worst step first dramatically reduces how much starting material you need to commit.

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