Percent Yield Calculator
Find the percent yield of a reaction from your actual and theoretical yield, or work out the theoretical yield first.
Quick answer: Percent yield = actual yield ÷ theoretical yield × 100. If a reaction could make 10.0 g of product and you collect 8.2 g, the percent yield is 8.2 ÷ 10.0 × 100 = 82%.
- Percent yield shows how much of the possible product you actually collected.
- The theoretical yield always comes from the limiting reactant.
- Results above 100% point to wet or impure product or a measuring mistake.
How to Calculate Percent Yield
- Write the balanced equation for the reaction.
- Find the limiting reactant and convert its mass to moles (mass ÷ molar mass).
- Find the theoretical yield: moles of limiting reactant × mole ratio × molar mass of product.
- Divide your actual yield by the theoretical yield.
- Multiply by 100 to get the percentage.
The last two steps are an ordinary percentage, part ÷ whole × 100, the same method used in our percentage calculator.
Worked Examples
Example 1: Both yields known
A student’s reaction has a theoretical yield of 10.0 g. After filtering and drying, they collect 8.2 g.
- 8.2 ÷ 10.0 = 0.82
- 0.82 × 100 = 82% yield
Example 2: Making water from hydrogen
The equation is 2H₂ + O₂ → 2H₂O. Hydrogen is the limiting reactant: 0.50 mol. The mole ratio of H₂O to H₂ is 2 ÷ 2 = 1, and the molar mass of water is 18.02 g/mol. The student collects 7.65 g of water.
- Theoretical yield: 0.50 × 1 × 18.02 = 9.01 g
- 7.65 ÷ 9.01 = 0.8491
- 0.8491 × 100 = 84.91% yield
Percent Yield Quick-Reference Table
Results for a reaction with a theoretical yield of 25.0 g:
| Actual yield (g) | Percent yield | Product lost (g) |
|---|---|---|
| 12.5 | 50% | 12.5 |
| 15.0 | 60% | 10.0 |
| 17.5 | 70% | 7.5 |
| 20.0 | 80% | 5.0 |
| 22.5 | 90% | 2.5 |
| 24.0 | 96% | 1.0 |
| 25.0 | 100% | 0 |
Why Your Yield Is Lower (or Higher) Than Expected
| Result | Common causes |
|---|---|
| Below 100% | Reaction did not finish, side reactions, product left on filter paper or glassware, losses during purification |
| Above 100% | Product still wet, impurities or unreacted chemicals mixed in, weighing error |
Tips for a Better Yield and Lab Grade
- Dry your product fully before weighing it; water adds mass and inflates the yield.
- Rinse glassware with a little solvent to recover product stuck to the sides.
- Double-check the limiting reactant. Using the wrong reactant is the most common mistake in theoretical yield.
- Report both numbers. Give the actual yield, the theoretical yield and the percentage, with units.
- Track your lab marks. Lab reports usually count toward your course grade. Check your running total with the average grade calculator or see what you need on the final with the final grade calculator.
Frequently Asked Questions
What is percent yield?
Percent yield tells you how much product a chemical reaction actually produced compared with the maximum amount it could produce. It is a measure of how efficient the reaction and your lab technique were.
How do you calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. For example, 8.2 g collected from a theoretical 10.0 g is 8.2 ÷ 10.0 × 100 = 82%.
How do you find the theoretical yield?
Find the limiting reactant, convert it to moles, multiply by the mole ratio of product to reactant from the balanced equation, then multiply by the molar mass of the product. Use the “Find theoretical yield” mode above to do this automatically.
Can percent yield be over 100%?
In theory, no. A result above 100% usually means the product still contains water or solvent, has impurities, or a mass was recorded incorrectly. It signals an error to discuss in your lab report.
Why is percent yield usually less than 100%?
Reactions may not go to completion, side reactions can make other products, and some product is always lost when filtering, transferring or purifying it.
What is a good percent yield?
There is no single cut-off. Yields vary with the reaction and your technique, and multi-step syntheses are usually much lower than one-step reactions. Your teacher or lab manual will say what is expected.
Do actual and theoretical yield need the same units?
Yes. Both must be in grams, or both in moles, before you divide. Mixing units gives a meaningless percentage.
What is the difference between percent yield and percent error?
Percent yield compares the product you made with the maximum possible product. Percent error compares any measured value with an accepted value. For the second, use the percent error calculator.
What is a limiting reactant?
The limiting reactant is the reactant that runs out first. It sets the maximum amount of product, so the theoretical yield is always calculated from it.