Percent Yield Calculator
Calculate percent yield instantly using actual and theoretical yield. Ideal for chemistry, lab work, education, and manufacturing quality-control.
What the percent yield calculator does
The percent yield calculator compares the amount of product you actually obtained from a reaction with the amount that stoichiometry says was possible. Enter the theoretical yield and the actual yield in the same unit, grams or moles, and press Calculate. The result is the percent yield, the standard measure of how efficient a synthesis or process was.
The formula
percent yield = (actual yield ÷ theoretical yield) × 100
If theory predicts 12.0 g and you isolate 9.6 g, the yield is 80%. Because it is a ratio, the units cancel; what matters is that both figures refer to the same product in the same unit.
Worked examples
| Reaction | Theoretical | Actual | Percent yield |
|---|---|---|---|
| Aspirin from salicylic acid | 2.61 g | 1.95 g | 74.7% |
| Silver chloride precipitation | 4.22 g | 4.15 g | 98.3% |
| Grignard addition | 8.40 g | 4.70 g | 56.0% |
| Ester hydrolysis (in moles) | 0.0500 mol | 0.0420 mol | 84.0% |
| Recrystallised product | 3.10 g | 3.25 g | 104.8% (see below) |
What a given yield means
| Percent yield | Interpretation |
|---|---|
| Above 95% | Quantitative; typical of precipitations and simple acid-base reactions |
| 80 to 95% | Very good for organic synthesis |
| 60 to 80% | Acceptable for multi-step routes and teaching labs |
| Below 50% | Poor; check for side reactions, moisture, or losses during work-up |
| Above 100% | Impossible; product is impure, wet, or the theoretical value is wrong |
In a multi-step synthesis yields multiply. Five steps at 80% each give an overall yield of 0.85 = 33%, which is why process chemists spend so much effort on each individual step.
Why yields fall short
- Equilibrium. Reversible reactions such as esterification stop well before completion unless a product is removed.
- Side reactions. Competing pathways consume reactant to make something else.
- Mechanical losses. Product stays on filter paper, in the flask, or in the mother liquor after recrystallisation.
- Impure or wet reagents. Water destroys Grignard reagents and anhydrides; old reagents have degraded.
- Incomplete reaction. Too little time or too low a temperature.
Why yields exceed 100%
A result above 100% does not mean the reaction created matter. It usually means the product still contains solvent or water, has unreacted starting material or by-products mixed in, or that the theoretical yield was calculated with the wrong limiting reactant. Dry the sample to constant weight, check its melting point or spectrum, and recheck the stoichiometry with the theoretical yield calculator.
Percent yield versus other efficiency measures
Percent yield says nothing about how much waste was generated. Atom economy, the fraction of reactant mass that ends up in the desired product according to the balanced equation, is the green-chemistry complement: an addition reaction has 100% atom economy, whereas a Wittig reaction discards most of its mass as triphenylphosphine oxide. Selectivity measures how much of the consumed reactant became the desired product rather than by-products. A process can have high selectivity and low yield if the reaction simply did not go to completion.
Common mistakes
- Swapping the two values. Actual goes on top. A yield over 100% from a clean product usually means the fields were reversed.
- Mixing units. Theoretical in grams and actual in moles gives nonsense.
- Weighing a wet product. Dry to constant mass before weighing.
- Using the excess reactant for the theoretical yield. Only the limiting reactant sets the maximum.
Related tools
The moles calculator and molar mass calculator feed the theoretical yield, the stoichiometry calculator handles the balanced-equation step, and the mass percent calculator and percent composition calculator help assess product purity.
External references
- LibreTexts: theoretical yield and percent yield
- ACS: principles of green chemistry, including atom economy
Frequently asked questions
What is a good percent yield?
Above 90% is excellent, 70 to 90% is good, and below 50% usually signals a problem with the procedure or purification.
Can I calculate percent yield in moles?
Yes, as long as both values are in moles. The ratio is identical to the mass-based figure for a single product.
How do I find the theoretical yield?
From the limiting reactant and the balanced equation. The theoretical yield calculator does this step.
Does purification lower the yield?
Yes. Recrystallisation and chromatography always leave some product behind, but they raise purity. Reported yields normally refer to purified product.
What is the overall yield of a multi-step synthesis?
The product of the individual step yields. Three steps at 90%, 75% and 80% give 0.9 × 0.75 × 0.8 = 54%.