Calculator
Percentage Yield Calculator
How much of the possible product you actually isolated from a laboratory preparation.
Yields
Units are normalised automatically — mg, g and kg can be mixed.
Mass of dry product weighed.
Maximum possible mass from the limiting reactant.
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Laboratory calculation card
Enter the actual and theoretical yields to see the percentage yield.
Percentage yield = (Actual yield / Theoretical yield) × 100
Both yields must be in the same unit before dividing. This page converts mg and kg to grams first, so 412 mg against a theoretical 0.520 g is (0.412 / 0.520) × 100 = 79.23%.
The actual yield is always a measured mass of dry product. The theoretical yield is calculated from the limiting reactant and the balanced equation — use the Theoretical Yield Calculator if you have not worked it out.
Worked example: Percentage yield of aspirin from salicylic acid
A student acetylates 3.00 g of salicylic acid with 5.0 mL of acetic anhydride (density 1.08 g/mL). After recrystallisation and drying to constant weight, 2.87 g of aspirin is weighed. Find the theoretical yield and the percentage yield.
- Salicylic acid (C₇H₆O₃)
- 3.00 g, 138.12 g/mol
- Acetic anhydride
- 5.0 mL × 1.08 g/mL, 102.09 g/mol
- Aspirin (C₉H₈O₄)
- 180.16 g/mol
- Actual yield (dry)
- 2.87 g
Moles of each reactant
Salicylic acid: 3.00 g ÷ 138.12 g/mol = 0.02172 mol Acetic anhydride: (5.0 × 1.08) g ÷ 102.09 g/mol = 0.05289 mol
Limiting reactant (1 : 1 equation)
0.02172 mol < 0.05289 mol, so salicylic acid is limiting
Theoretical yield
0.02172 mol × 180.16 g/mol = 3.913 g aspirin
Percentage yield
(Actual ÷ Theoretical) × 100 = (2.87 g ÷ 3.913 g) × 100 = 0.733453 × 100 = 73.35 %
Product not recovered
3.913 g − 2.87 g = 1.043 g (26.65 %)
Theoretical yield = 3.913 g; percentage yield = 73.35 %.
About three-quarters of the aspirin the salicylic acid could form was isolated as dry solid; the rest was lost to incomplete reaction, to the mother liquor during recrystallisation and to transfers. A yield in this range is typical of a single-recrystallisation student preparation. The number says nothing about purity: a damp or contaminated product can give a higher yield, so record a melting point or a TLC alongside it.
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References
- Furniss BS, Hannaford AJ, Smith PWG, Tatchell AR. Vogel's Textbook of Practical Organic Chemistry. 5th ed. Harlow: Longman Scientific & Technical; 1989.
- International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (the 'Gold Book'). Source
Common questions
The solid weighed more than pure product could. It is almost always still damp or holding solvent, contaminated with a reagent or by-product, or the theoretical yield is wrong — for example the anhydrous MW was used for a hydrate. Dry to constant weight, check the melting point, and recheck the theoretical yield.
It depends on the reaction and how many purification steps there are. A single recrystallisation typically costs 10–30% of the product, so yields of 60–85% are common for simple preparations such as aspirin. Purity matters as much as the number.
Two decimal places for the percentage is standard for a student record, and no more precise than your balance allows. Keep full precision during the calculation and round only the final answer.
No. Yield compares product formed with what the reaction could form. Recovery compares what you got back with what you started with of the same substance — for example after an extraction or recrystallisation.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy