Percent yield calculator
Find the percent yield of a reaction, or work backward to the actual or theoretical yield. Answers are rounded to the right number of significant figures.
The percent yield formula
Percent yield = (actual yield ÷ theoretical yield) × 100
The actual yield is what you measured in the lab. The theoretical yield is the most product the reaction could make, calculated from the limiting reactant.
Worked example
10.0 g of aluminum can make at most 18.9 g of Al₂O₃ (4Al + 3O₂ → 2Al₂O₃). If you collect 15.0 g, the percent yield is 15.0 ÷ 18.9 × 100 = 79.4%.
Finding the theoretical yield
- Balance the equation (try the equation balancer).
- Convert each reactant’s mass to moles with its molar mass.
- Use the mole ratio to find which reactant makes the least product. That’s the limiting reactant.
- Convert those moles of product back to grams.
Why yields are below 100%
Product is lost during transfers and filtering, reactions don’t always go to completion, and side reactions make other products. A yield over 100% usually means the product was still wet or contained impurities.
Common questions.
Can percent yield be over 100%?
Not in reality. A calculated value over 100% points to a measurement problem, most often a product that wasn’t fully dried, or impurities that added mass.
What units should I use?
Any mass unit, as long as the actual and theoretical yields use the same one. Moles work too, since the ratio is the same.
How many significant figures should the answer have?
Percent yield is a division, so it keeps the fewest significant figures of the two yields. 15.0 g ÷ 18.9 g gives three: 79.4%.
What is a good percent yield?
It depends on the reaction. In teaching labs, 70–90% is common. Multistep syntheses often have much lower overall yields.