A percent yield and theoretical yield calculator for chemistry
This percent yield calculator does the whole stoichiometry in one place. Type the reaction, even unbalanced, enter how much of each reactant you used, and it balances the equation, finds the limiting reactant, works out the theoretical yield of the product you choose and, once you enter what you actually collected, the percent yield. It also shows how much of each excess reactant is left over.
It is aimed at chemistry students writing up a practical and at anyone checking a synthesis on paper. Masses can be in g, mg or kg, or amounts in mol, and formulas may contain brackets and hydrates. Calculations run in your browser using IUPAC atomic weights.
How to use the theoretical yield calculator
- Type the reaction, for example
N2 + H2 -> NH3, or press one of the examples. The balanced equation appears underneath. - Enter the amount of each reactant and choose its unit. Leave a reactant empty if it is in excess.
- Pick the product wanted if the reaction has more than one.
- Enter your actual yield to get the percent yield, or leave it empty to see only the theoretical yield.
- Already know both yields? Choose Percent yield only and enter them.
Theoretical & Percent Yield Calculator features
Balances for you
The same exact balancer as the chemical equation balancer, so 2Al + 3Cl₂ → 2AlCl₃ is worked out automatically.
Limiting reactant
Compares moles ÷ coefficient for every reactant you enter and highlights the smallest.
Excess left over
Grams of each excess reactant remaining when the limiting one runs out.
Any product
Choose which product to report, in grams or moles.
Quick mode
A plain actual ÷ theoretical × 100 calculator for when you already have the theoretical yield.
Percent yield and theoretical yield formulas
Percent yield = actual yield ÷ theoretical yield × 100. The theoretical yield is the mass of product the limiting reactant could make if the reaction went to completion: convert each reactant to moles, divide by its coefficient, take the smallest value, multiply by the product’s coefficient and its molar mass.
Worked example: 28.0 g of N₂ (28.014 g/mol) is 0.9995 mol, and 10.0 g of H₂ (2.016 g/mol) is 4.960 mol. In N₂ + 3H₂ → 2NH₃ the ratios are 0.9995 ÷ 1 and 4.960 ÷ 3 = 1.653, so nitrogen is limiting. It can make 2 × 0.9995 = 1.999 mol of NH₃, which is 34.04 g. If 25.0 g of ammonia is collected, the percent yield is 25.0 ÷ 34.04 × 100 = 73.4%, and 3.96 g of hydrogen is left over.
Why yields are below 100%
- Reversible reactions such as ammonia synthesis stop at equilibrium.
- Side reactions make by-products instead of the product you want.
- Product is lost in filtering, transferring and recrystallising.
- A yield above 100% almost always means wet or impure product, not extra product.
Limiting reactant in common lab reactions
| Reaction | Amounts | Limiting | Theoretical yield |
|---|---|---|---|
| N₂ + 3H₂ → 2NH₃ | 28 g N₂, 10 g H₂ | N₂ | 34.04 g NH₃ |
| Fe₂O₃ + 3CO → 2Fe + 3CO₂ | 100 g Fe₂O₃, 50 g CO | CO | 66.46 g Fe |
| 2Al + 3Cl₂ → 2AlCl₃ | 2.70 g Al, 4.05 g Cl₂ | Cl₂ | 5.08 g AlCl₃ |
| C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ | 100 g glucose | Glucose | 51.14 g ethanol |
Theoretical & Percent Yield Calculator FAQ
How do I calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. For 25.0 g obtained out of a possible 34.04 g, the percent yield is 73.4%.
How do I find the theoretical yield in chemistry?
Balance the equation, convert each reactant to moles, divide by its coefficient to find the limiting reactant, then multiply its moles by the product-to-reactant mole ratio and the product’s molar mass.
What is a limiting reactant?
The reactant that runs out first. It sets the maximum amount of product; the others are in excess and some of them is left over.
Can percent yield be more than 100%?
Not for a pure, dry product. Results above 100% point to solvent or water left in the product, impurities, or a weighing error.
Do I need to balance the equation first?
No. This theoretical yield calculator balances it for you and shows the coefficients it used.
Is this percent yield calculator for chemistry homework accurate?
It uses exact balancing and IUPAC 2021 atomic weights, so answers match textbook methods; small differences come from rounding of atomic masses in different books.