Percent Yield Calculator
Enter the actual and theoretical yield to get the percent yield, or give a reaction and the amount of each reactant and let the calculator find the limiting reactant and theoretical yield for you. It shows the working, how much product was not recovered, and a plain-language note on what a result above or below 100 % usually means. Runs entirely in your browser. Free, no sign-up.
The most product the limiting reactant could make.
What you measured, in the same unit.
Results
75.5 %
Percent yield
56.3 g
Theoretical yield
42.5 g
Actual yield
13.8 g
Not recovered
Yields below 100 % are normal. Typical reasons are a reaction that is reversible or incomplete, side reactions that use up reactant, and product lost on transfer, filtering, washing and purification.
Rounded to 3 significant figures, the fewest in the values you entered.
The working
Percent yield = actual ÷ theoretical × 100 = 42.50 g ÷ 56.30 g × 100 = 75.5 %
How to Use the Percent Yield Calculator
- 1. Choose how you know the theoretical yield. If your lab handout or earlier calculation gave it, pick I already have it. Otherwise pick Work it out from the reactants.
- 2. Enter the numbers. With a known theoretical yield, type both yields in one unit. From the reactants, enter the equation, the amount of each reactant, the product you collected and your actual yield. Leave a reactant blank if it is in unlimited supply.
- 3. Read the percent yield. The result shows the percentage, the amount of product not recovered, and a note on what the figure means.
- 4. Check the working. The last box repeats the arithmetic, including the limiting reactant and the theoretical yield when they were calculated.
The Percent Yield Formula
The theoretical yield is the most product the limiting reactant could form if the reaction went to completion with no losses. The actual yield is the amount you really collected and weighed. The percent yield compares them:
Percent yield
actual yield ÷ theoretical yield × 100 %
Units
Both yields in the same unit (g with g, mol with mol)
The ratio is dimensionless, so any consistent unit works. If your theoretical yield is in grams and your actual yield in moles, convert one first. When the theoretical yield comes from the reactants, the calculator uses the same limiting-reactant method as the Limiting Reactant Calculator and converts the answer into the unit you chose.
Worked Examples
Known theoretical yield. The calculator opens with a theoretical yield of 56.3 g of ammonia and an actual yield of 42.5 g. Then 42.5 ÷ 56.3 × 100 = 75.5 %, and 13.8 g of ammonia was not recovered.
From the reactants. Aspirin is made from salicylic acid and acetic anhydride in a 1:1 ratio, C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + C₂H₄O₂. Start with 2.00 g of salicylic acid (138.122 g/mol) and leave the anhydride blank because it is in excess:
- Moles of salicylic acid: 2.00 g ÷ 138.122 g/mol = 0.01448 mol, so salicylic acid is limiting
- Moles of aspirin possible: 0.01448 mol × (1 ÷ 1) = 0.01448 mol
- Theoretical yield: 0.01448 mol × 180.159 g/mol = 2.61 g
- If you collect 1.85 g: 1.85 ÷ 2.61 × 100 = 70.9 %
Why a Yield Is Not 100 %
- Incomplete or reversible reactions. Some reactant never converts because the reaction reaches equilibrium first.
- Side reactions. Part of the reactant forms by-products instead of the product you want.
- Losses in handling. Product sticks to glassware or is left in the filtrate, wash liquid or recrystallisation solvent.
- Impure product. A product that still carries reactant or by-product weighs more than the pure compound, which can push the calculated yield up.
A yield above 100 % is a warning
For a dry, pure product the actual yield cannot beat the theoretical one. A result above 100 % usually means the product is still wet with solvent or water, is contaminated, or was weighed wrongly, or that the wrong reactant was treated as limiting. The calculator flags it instead of quietly rounding it down.
Frequently Asked Questions
- What is the formula for percent yield?
- Percent yield = (actual yield ÷ theoretical yield) × 100 %. The actual yield is what you measured, and the theoretical yield is what the balanced equation predicts from the limiting reactant. Both must be in the same unit.
- How do you calculate the theoretical yield?
- Balance the equation, convert each reactant to moles, divide by its coefficient to find the limiting reactant, then multiply that quotient by the product's coefficient and its molar mass. Choose the second mode of this calculator to have each step done for you.
- Can percent yield be over 100 %?
- Not for a pure, dry product, so a value above 100 % points to a problem. The usual causes are leftover solvent or water, impurities or by-products in the sample, a weighing error, or a wrongly identified limiting reactant. Dry the product to constant mass and recheck.
- What is a good percent yield?
- It depends on the reaction. Simple one-step preparations can approach a high yield, while multi-step syntheses lose product at each stage, so the fair comparison is with the range your procedure or textbook gives for that reaction.
- What is the difference between percent yield and percent error?
- Percent yield measures how much of the possible product you recovered. Percent error measures how far a measured value is from an accepted one, as |measured − accepted| ÷ accepted × 100. A yield of 80 % is a loss of 20 % of the product, not a 20 % error in a measurement.
- Do I need to use grams?
- No. The ratio is the same in any consistent unit, so you can compare moles with moles, or litres of gas with litres of gas. This calculator accepts mg, g, kg, mmol, mol, mL and L, and converts through the molar mass or molar volume when it works the theoretical yield out for you.