Percent Yield Calculator

Find the Percent Yield of a Reaction

Percent Yield Formula

Formula

\[ \%\,Yield = \frac{Y_a}{Y_t} \times 100 \]

Where:

\(Y_a\) — actual yield: the amount of product you actually obtained from the reaction
\(Y_t\) — theoretical yield: the maximum amount of product predicted by stoichiometry, assuming the reaction goes to completion with no losses

The formula expresses the efficiency of a chemical reaction: how close the amount of product you recovered in the lab came to the maximum amount the balanced equation allowed.

Percent Yield – Calculation Example

Example: a synthesis was predicted by stoichiometry to produce 10 g of product, but after purification you recovered 8.5 g.

\[ \%\,Yield = \frac{8.5\ \text{g}}{10\ \text{g}} \times 100 = 0.85 \times 100 = 85\% \]

\[ \Delta Y = 10\ \text{g} - 8.5\ \text{g} = 1.5\ \text{g} \]

Result: the percent yield is 85%, and the yield difference is 1.5 g — the amount of product lost or not formed.

How to Use the Percent Yield Calculator

Enter the Actual Yield — the measured amount of product you obtained (the default is 8.5).
Choose the unit for the actual yield from the dropdown: g, mg, kg, lb or oz.
Enter the Theoretical Yield — the maximum amount of product predicted by the stoichiometry of your balanced equation (the default is 10).
Choose the unit for the theoretical yield. It does not need to match the actual yield unit; the calculator converts both to grams internally.
Read the Percent Yield (in %) and the Yield Difference (Theoretical − Actual), shown in the unit of your actual yield.

What Is Percent Yield?

Percent yield is a measure of how efficient a chemical reaction is in practice. When you write a balanced chemical equation, stoichiometry tells you the maximum amount of product that could form if every reactant molecule converted perfectly and nothing was lost. That maximum is the theoretical yield. In the real world, reactions rarely behave ideally: side reactions consume starting material, equilibria stop before completion, and mechanical losses occur during filtration, transfers and purification. The amount you actually isolate is the actual yield.

Dividing the actual yield by the theoretical yield and multiplying by 100 gives a percentage that is easy to compare across experiments, scales and procedures. A yield of 100% means you recovered every bit of product the equation allowed — a practical impossibility for most reactions. Typical organic syntheses fall between 40% and 90%, while simple inorganic preparations or industrial processes optimized over decades can exceed 95%.

Interpreting the result matters as much as calculating it. A low percent yield signals losses somewhere: incomplete reaction, poor recovery during workup, impurities, or an error in the theoretical yield calculation itself. A yield above 100% is a red flag — it almost always means the product is contaminated with solvent or by-products, or that the theoretical yield was calculated from the wrong limiting reagent.

Assumptions, Limitations and Practical Tips

Units must describe the same product. The actual and theoretical yields must both refer to the same chemical substance, in the same state of purity. Comparing a wet, impure sample against a pure theoretical yield inflates the result.
Convert units before comparing, or let the calculator do it. Because the ratio is dimensionless, both yields in the same unit give the correct answer. This calculator converts g, mg, kg, lb and oz to grams automatically, so mixed units are fine.
The theoretical yield must be based on the limiting reagent. If you are unsure which reactant limits the reaction, balance the equation and compare mole ratios first — our Chemical Equation Balancer and Convert Atoms to Moles calculator can help.
A percent yield over 100% is not a bonus. Treat it as a signal to check purity (residual solvent, water of hydration, unreacted starting material) rather than as a success.
The yield difference tells you the scale of the loss. The calculator reports \(\Delta Y = Y_t - Y_a\) in grams, milligrams or whichever unit you chose for the actual yield — useful when deciding whether improving recovery is worth the effort.
Keep a consistent basis for mass. If your product is a hydrate or contains residual solvent, decide whether yields are quoted on a dry or as-is basis and stay consistent when comparing runs.

Percent yield is one of the most quoted numbers in lab reports and process chemistry because it captures reaction efficiency, workup quality and practical skill in a single figure. Pair it with stoichiometry tools such as the Atomic Mass calculator when deriving the theoretical yield from molar masses, and you have a complete workflow for reporting any synthesis.

Frequently Asked Questions

How do I calculate percent yield by hand?

First, find the theoretical yield from the balanced equation: identify the limiting reagent, convert its mass to moles, use the mole ratio to find moles of product, then convert back to grams. Divide the actual yield (in the same unit) by the theoretical yield and multiply by 100: \( \%Yield = \frac{Y_a}{Y_t} \times 100 \). Example: 4.2 g recovered from a predicted 6.0 g gives \( \frac{4.2}{6.0} \times 100 = 70\% \).

What is a good percent yield in chemistry?

It depends on the type of reaction. Simple inorganic preparations and finely optimized industrial processes can reach 95% or higher. Typical organic syntheses fall between 40% and 90%, and many multi-step sequences average 50–60% per step. In teaching labs, anything above 70% is often considered acceptable. The key is comparing your result to what the procedure and literature typically achieve, not to an arbitrary number.

Why is my percent yield over 100% and is that possible?

A true yield above 100% is chemically impossible, so it always signals a problem. The most common causes are a wet or impure product (residual solvent, water, drying agent, or unreacted starting material adding mass) or a theoretical yield calculated from the wrong reagent. Dry the sample thoroughly, check purity, and verify that your limiting reagent and stoichiometry were correct before accepting the number.

Do the actual and theoretical yields need to be in the same unit?

No. Because percent yield is a ratio, both values just need to describe the same substance in comparable mass terms. The calculator converts g, mg, kg, lb and oz to grams automatically, so you can enter mixed units. If you compute by hand, convert both to the same unit first: 1 lb = 453.59237 g and 1 oz = 28.3495 g.

What is the difference between actual yield, theoretical yield and percent yield?

Theoretical yield is the maximum product predicted by stoichiometry, assuming the limiting reagent reacts completely with no losses. Actual yield is what you physically isolate and weigh after the reaction and purification. Percent yield is the ratio of the two, expressed as a percentage — a measure of how much of the possible product you actually recovered. Percent yield is dimensionless; the other two are masses.

Can percent yield be negative or zero?

Zero is possible in principle — it means no product was isolated at all, usually due to a failed reaction or a catastrophic error in the workup. A negative value is impossible because you cannot recover less than zero product. If your calculation produces a negative number, check that you have not swapped actual and theoretical yields in the formula.

What are the most common mistakes when calculating percent yield?

The top errors are: using the excess reagent instead of the limiting reagent to find the theoretical yield; forgetting to balance the chemical equation first; comparing yields of different substances or purity states (e.g., a hydrate against an anhydrous prediction); and mixing units without converting. Also double-check molar masses — a wrong atomic mass propagates directly into the theoretical yield and skews the final percentage.