What Is Percent Yield and How Is It Calculated?
Percent yield is the ratio of the actual mass of product collected from a chemical reaction to the maximum mass the stoichiometry allows (the theoretical yield), multiplied by 100. It measures how efficiently a reaction converted reactants into product, and it can never exceed 100% for a pure, dry product.
The percent yield formula is: percent yield = (actual yield ÷ theoretical yield) × 100. The theoretical yield comes from the balanced equation: find moles of each reactant (mass ÷ molar mass), divide each by its coefficient, and the smaller result is the limiting reagent. Then theoretical yield = limiting moles ÷ coefficient × product coefficient × product molar mass.
The International Union of Pure and Applied Chemistry (IUPAC) defines the mole as exactly 6.02214076 × 10²³ elementary entities (since the 2019 SI redefinition), which is the basis for every stoichiometric yield calculation. Many undergraduate organic labs consider a percent yield above roughly 70% good, while multi-step pharmaceutical syntheses often report overall yields well below 50%.
How to Use This Percent Yield Calculator
Balance your equation first, then enter the data for two reactants and the product. The limiting reagent, theoretical yield, and percent yield update instantly.
- Mass (g): How much of each reactant you started with, in grams.
- Molar mass (g/mol): Sum of atomic masses for the compound; use our Molar Mass Calculator if unsure.
- Coefficient: The stoichiometric number in front of the species in the balanced equation (use 1 if none is written).
- Actual yield (g): The mass of product you really collected. Leave blank to see only the theoretical yield and limiting reagent.
All masses are in grams and molar masses in g/mol, the SI-consistent convention used in chemistry courses worldwide. For ionic or hydrated compounds, include the water of crystallisation in the molar mass.
What Does Your Percent Yield Mean?
The table below gives a rule-of-thumb interpretation of percent yield. Acceptable values depend heavily on reaction type and the number of purification steps.
| Percent yield | Typical interpretation |
|---|---|
| 90–100% | Excellent; very efficient reaction and careful recovery |
| 70–90% | Good; typical of well-run lab syntheses |
| 40–70% | Moderate; losses in transfer, side reactions, or equilibrium limits |
| Below 40% | Low; review conditions, purity of reagents, and technique |
| Above 100% | Impure or wet product, or an error in masses or the equation |
Frequently Asked Questions
What is a good percent yield?
A percent yield of 70–90% is generally considered good for a laboratory synthesis, and above 90% is excellent. Multi-step industrial and pharmaceutical processes accept lower per-step yields because losses compound across steps.
How do you find the limiting reagent?
Convert each reactant mass to moles by dividing by its molar mass, then divide each by its coefficient in the balanced equation. The reactant with the smallest result is the limiting reagent because it runs out first and caps the amount of product.
Can percent yield be over 100%?
Not for a pure, dry product. A calculated yield above 100% means the isolated solid still holds solvent, water, or impurities, or that a mass, molar mass, or coefficient was entered incorrectly. Dry the product fully and re-weigh it.
What is the difference between percent yield and percent error?
Percent yield compares the product you collected with the theoretical maximum from stoichiometry, measuring reaction efficiency. Percent error compares a measured value with an accepted value, measuring measurement accuracy. They use different formulas and answer different questions.