Percent Yield Calculator | Actual vs Theoretical Yield

What is a percent yield calculator?

A percent yield calculator compares the actual yield of a chemical reaction to its theoretical yield and expresses the result as a percentage. Percent yield shows how much product a reaction actually produced compared with the maximum amount predicted by stoichiometry.

Percent yield formula

Percent yield equals actual yield divided by theoretical yield, multiplied by 100:

$\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

• Actual yield is the mass of product collected after a reaction and purification, usually measured in grams.
• Theoretical yield is the maximum mass of product a reaction can form, calculated from the balanced equation and the limiting reactant (the reactant that runs out first).

The calculator on this page updates the result as soon as both values are entered. No button needs to be pressed.

How to calculate percent yield

1. Balance the chemical equation for the reaction.
2. Identify the limiting reactant.
3. Use stoichiometry to calculate the theoretical yield from the limiting reactant.
4. Weigh the dried, purified product to find the actual yield.
5. Divide actual yield by theoretical yield and multiply by 100.

Example calculations

Example 1: Aspirin synthesis

A student synthesizing aspirin calculates a theoretical yield of 5.42 g. After purification, the student collects 4.65 g of dried product.

Percent yield = (4.65 / 5.42) × 100 = 85.79%

Example 2: Ammonia production

A plant using the Haber process has enough nitrogen and hydrogen for a theoretical yield of 850 kg of ammonia. The plant actually produces 765 kg.

Percent yield = (765 / 850) × 100 = 90.00%

Example 3: Low-yield synthesis

A multistep synthesis has a theoretical yield of 2.75 g. Only 0.82 g of pure product is isolated after purification.

Percent yield = (0.82 / 2.75) × 100 = 29.82%

Why percent yield is usually below 100%

Percent yield is almost always below 100% because of losses that happen during a real reaction:

• Some reactant molecules do not react completely.
• Side reactions form unwanted byproducts instead of the target product.
• Product is lost during filtration, recrystallization, or when it is transferred between containers.
• The balance used to weigh the product has a small margin of error.
• Reversible reactions stop before all reactants have converted to product.

A yield of 100% would mean every reactant molecule turned into pure product with no losses. That rarely happens outside simple, well-optimized reactions.

Can percent yield be above 100%?

No. Product mass cannot exceed the theoretical maximum. A calculated result above 100% almost always means the weighed sample contains something other than the pure product, such as leftover solvent, unreacted starting material, or moisture absorbed from the air. Drying the sample further and reweighing usually brings the value back under 100%.

Zero, negative, and invalid values

• If actual yield is 0 g, percent yield is 0%.
• Theoretical yield must be greater than zero. The calculator will not produce a result if theoretical yield is zero or negative, because dividing by zero is undefined.
• Actual yield cannot be negative. A negative entry is rejected and an error message is shown instead of a result.

Frequently asked questions

What is percent yield in chemistry?

Percent yield is the ratio of actual yield to theoretical yield, expressed as a percentage. It shows how much of the maximum possible product a reaction actually produced.

What is a good percent yield?

It depends on the reaction. Simple, single-step reactions often reach 85% to 95%. Multistep organic syntheses commonly fall between 40% and 70%, because product is lost at every step.

Why is my percent yield over 100%?

The product is probably not pure. Common causes are leftover solvent, unreacted starting material, or moisture absorbed from the air. A pure product cannot have a percent yield above 100%.

What is the difference between actual yield and theoretical yield?

Actual yield is the amount of product measured after a reaction and purification. Theoretical yield is the maximum amount predicted by the balanced equation, assuming every reactant converts to product with no losses.

How is theoretical yield calculated?

Theoretical yield comes from the balanced chemical equation. The mass of the limiting reactant is converted to moles, then to moles of product using the mole ratio from the equation, then to grams using the molar mass of the product.

What is the difference between percent yield and atom economy?

Percent yield compares the actual product mass from one experiment to the theoretical maximum for that experiment. Atom economy compares the mass of the desired product to the total mass of all reactants in the balanced equation, and measures how efficient the reaction itself is, separate from losses during handling and purification.